How to Make a Custard-Filled Cake With Mousse Frosting

Updated on January 3, 2020
Joan Dragonfly profile image

I was frustrated with buying expensive mediocre sheet cakes from the store until I discovered a way to make the best DIY cake ever!

DIY Cake Decorating
DIY Cake Decorating | Source

Forget the Standard Sheet Cake

Have you noticed how expensive a standard store-bought sheet cake can be? Why bother with a mediocre cake, when you can make the most delicious cake yourself? For this perfect DIY cake, all you’ll need is a box cake mix, homemade custard, mousse frosting, and voilà . . . you have a delectable and visually appealing cake (even without decorating it)! Add these recipes together (cake, custard, and frosting) to create the perfect do-it-yourself cake for any occasion! You’ll wonder why you hadn’t thought of it sooner. I had recently made one of these cakes for a party and got compliments from guests that I’ve never even met before! It was delicious, not too rich, light and airy, and very satisfying. I liked the cake so much that I made three different cakes for yet another party (one all white, one all chocolate, and one Boston creme-style). A guest at this second party told me that it was the best cake that they ever tasted! I definitely agree. The kids were begging for dessert, once they saw me take the cakes out of the refrigerator! Try This DIY delectable recipe!

Box Cake Mix With Ingredients
Box Cake Mix With Ingredients | Source

Step 1: Choose Cake Type and Gather Ingredients

Below you'll find combined lists of cakes, fillings, and frostings to choose from, along with a general list of ingredients to gather before baking, but make sure to read each of the actual recipes themselves for specific quantities of each ingredient, so you can be sure to have exactly what is needed. The list below is just a quick checklist. Also, make sure to check that no one who will be eating (or coming into contact with) your delectable DIY cake has any food allergies.

Boston Cream-Style

(Yellow Cake, Custard Filling, and Chocolate Frosting)

  • Boxed yellow cake mix
  • Milk
  • Sugar
  • Flour
  • Salt
  • Eggs
  • Vegetable Oil
  • Water
  • Vanilla Extract
  • 1 (3.9 oz) package instant chocolate pudding mix
  • 1 (8 oz) container whipped topping

Reverse Boston Cream

(Chocolate Cake, Custard Filling, and Vanilla Frosting)

  • Boxed chocolate cake mix
  • Milk
  • Sugar
  • Flour
  • Salt
  • Eggs
  • Vegetable Oil
  • Water
  • Vanilla Extract
  • 1 small carton of heavy whipping cream
  • 1 (3.5 oz) package instant vanilla pudding mix
  • 1 (8 oz) container whipped topping

Triple Chocolate

(Chocolate Cake, Pudding Filling, and Mousse Frosting)

  • Boxed chocolate cake mix
  • Eggs
  • Vegetable Oil
  • Water
  • Milk
  • 2 (3.9 oz) packages instant chocolate pudding mix
  • 1 (8 oz) container whipped topping

White and Fluffy

(White Cake, Custard Filling & White Whipped Frosting)

  • Boxed white cake mix
  • Milk
  • Sugar
  • Flour
  • Salt
  • Eggs
  • Vegetable Oil
  • Water
  • Vanilla Extract
  • 1 carton of heavy whipping cream
  • 1 (3.5 oz) package instant vanilla pudding mix
  • 1 (8 oz) container whipped topping

Bake it, trim it, and freeze it.
Bake it, trim it, and freeze it. | Source

Step 2: Bake the Cake

Bake the cake according to the directions on the back of the box of cake mix, trim the top rounded and protruding section off of ONE of the cakes after taking them out of the oven, so that the bottom layer (once stacked) won't have a rounded top to interfere with the forthcoming custard filling, and then place the cake layer (with the trimmed top) in the freezer for a few short hours, until it is stiff enough to add the layer of custard on top of it (to prevent it from getting soggy).

  • Bake: Two cake layers (both in their own pans), using either a store-bought cake mix or if you have time to spare, go all out and use a homemade cake recipe. For example, to bake a basic vanilla cake from scratch, follow these easy steps: gather ingredients (2 sticks butter, 3 cups flour, 1 tsp baking powder, 1/2 tsp salt, 1 1/4 cup sugar, 4 eggs, 1tbsp vanilla, 1 1/4 cup milk). Preheat oven to 350. Grease 2 round cake pans. In one bowl, combine flour, baking powder, and salt. In another bowl, beat 2 sticks softened butter and sugar with a mixer for 3 mins. Then be beat in eggs, milk, and vanilla. Combine and beat (a little at a time) the dry mix from one bowl into the wet mix in the other bowl. Pour batter into both cake pans. Bake until done (approx. 30–35 mins). Test with a toothpick. Allow cakes time to cool before removing from pans.
  • Trim: For the cake that you intend to use as the bottom layer, trim off the top section, so that it is flat enough to add the custard on top of it, later.
  • Freeze: Place the bottom cake layer uncovered in the freezer for an hour to keep it firm enough to eventually add custard on top.

Making Custard Cake Filling
Making Custard Cake Filling | Source

Step 3: Make the Custard

Follow the instructions carefully when making the custard, since it can be tricky to get the right consistency. If it doesn't seem firm enough, then it may need more stirs and a few more minutes in the microwave (done in small increments of time). It should become a little more firm each time you remove it from the microwave.

  • Recipe: Find your favorite custard recipe or try this easy custard cake filling recipe. First, gather the ingredients (2 cups milk, 3/4 cups sugar, 5 tbsp white flour, 1/4 tsp salt, 2 eggs, 1 tsp vanilla), heat milk in the microwave until hot (not boiling). In another bowl, add sugar, flour, salt. Slowly whisk milk into sugar mixture, a little at a time, until evenly blended. Cook milk mixture in the microwave in 1-minute increments and then stir between each interval (this is very important to do this step right, so please be patient). The custard should start to thicken and could take up to 5 minutes (or more) to get a good firm consistency. Next, whisk eggs in a bowl by itself, then add 1/3 cup milk mixture in with the eggs and whisk. Gradually add in the rest of the milk mixture in with the eggs to form the custard. Heat custard in the microwave for about 2 minutes or so until it has thickened. Allow to cool and finally stir in vanilla.
  • Filling: Spread the custard filling on top of the bottom (frozen) cake layer.
  • Freeze: Place custard filling on top of the frozen cake layer back in the freezer (uncovered for more 2 hours), until custard is frozen.

Stacking Cake Layers
Stacking Cake Layers | Source

Step 4: Build the Cake

Now it is time to stack the layers with the custard filling in the middle (as shown in the photo above).

  • Bottom Layer: Take bottom custard-covered cake layer out of the freezer.
  • Top Layer: Place (untrimmed) top cake layer on top of the custard layer.
  • Chill: Place the layer cake back in the freezer until finished with step 5 (below).

Mousse Frosting
Mousse Frosting | Source

Step 5: Make the Mousse Frosting

Making the mousse frosting is so easy and fun! Nothing is more satisfying than watching this whipped frosting keep its shape, as you spread it on your delicious double layer cake. Before you get too far into this project, you may want to clean out a big enough space in your refrigerator to keep the cake in. Because of the mousse frosting and custard, this cake must stay refrigerated before serving.

  • Recipe: Choose your favorite mousse frosting recipe, such as Vanilla Whipped Cream or Chocolate Mousse Frosting. For example, to make a white whipped cream mousse frosting, gather ingredients (1 cup whipping cream, 2 tsp vanilla, 3.5 oz box of instant vanilla pudding, 1/4 cup milk, 1 tsp vanilla, 3 cups or 1 container of whipped topping from your grocer’s freezer aisle), in a large bowl, beat milk, vanilla, whipping cream, and pudding mix with a mixer for 2 minutes. Fold in whipped topping until well blended.
  • Refrigerate: Chill the frosting in a refrigerator before spreading.
  • Spread: When mousse frosting is firm, spread it onto the cake.

Decorate Cakes with Fruit
Decorate Cakes with Fruit | Source

Step 6: Decorating the Cake

There are so many different ways to decorate a cake. The best rule of thumb is to keep it simple. You don't want your labor of love to look totally cheesy because decorating got a little out of hand. Here are some different methods of cake decorating to choose from.

When I first brainstormed cake decorating ideas, I considered creating floral decorations made of frosting myself (see video below), but the more I practiced (not on my cake, thankfully), the more patience I lost, so I ended up cheating and purchased pre-made sweet edible candy flowers and beads to plunk on top my cakes at the last minute. Only the leaves were created with green food coloring mixed with white whipped frosting placed inside a decorating bag with a leaf-shaped tip piping nozzle. They made all the difference in helping my cakes look professional (see a photo of the three cakes below)!


The finished cake will need to be kept refrigerated for the custard filling to stay firm enough to hold up the cake’s upper layer, so take the cake out of the fridge no longer than a half-hour, prior to serving.

Three Delicious DIY Cakes
Three Delicious DIY Cakes | Source

Cake Miniatures: A Neat Craft for Kids

This is a fun and easy activity for kids. They can even take their mini cakes home with them when they're done.

  • Practice: Once you’ve made a cake like this yourself, teach the kids!
  • Activity: The kids will love decorating their own miniature cake.
  • Mini Pans: Use mini cake pans and precook multiple mini cakes.
  • Cake Shaping: Bake, cut up, and build unique cake shapes and animals.
  • Bulk: Make the cake, filling, and frosting ahead of time in large batches.
  • Watch and Learn: Watch how-to videos on cake decorating.
  • Decorate: Use cake decorating kits that are easy for kids to use.
  • Takeaway: Mini cake boxes may be needed for kids to take home.

Kids' Mini Cake to Decorate
Kids' Mini Cake to Decorate | Source

Themes: Cake Decorating Ideas for Any Occasion


• Mother's Day (flowers, gift boxes)
• Father's Day (tie, tools, nature, fishing)
• Grandparent's Day (family tree, handprint)
• Halloween (candy corn, spooky stuff)
• Thanksgiving (turkey, cornucopia)
• Christmas (pine tree, gift, snowflakes)
• Chanukah (dreidels, candles)
• Kwanzaa (red, black, green candles)
• St. Patrick's Day (rainbow, pot of gold)
• Easter (bunny, colored eggs, chicks)
• New Years (clock, fireworks, confetti)
• 4th of July (flag, fireworks, confetti)
• Valentine's Day (hearts, roses)

Special Occasions

• Birthdays (flowers, balloons)
• Anniversary (flowers, ribbons, confetti)
• Encouragement (thumbs up)
• Accomplishments (mountain peak)
• Engagement (ring, flowers, silhouettes)
• Hero (star, burst, medal)
• Welcome Home (banner, house, ribbon)
• Wedding (flowers, ribbon, bride & groom)


• New Baby (baby, stork, blocks, rattles)
• New Home (house, white picket fence, mailbox)
• Graduation (cap, diploma, wise owl)
• New Job (briefcase)

Video: Dahlia and Rose Cake Flower Decorating

POLL: DIY Cake with Mousse Frosting and Custard Filling

If you've tried one of these recipes, what occasion did you make the cake for?

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This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Questions & Answers

    © 2017 Joan Dragonfly


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      • Joan Dragonfly profile imageAUTHOR

        Joan Dragonfly 

        7 months ago from New England

        I've never tried to freeze the finish product, so I'm not sure.

      • profile image

        Tiara S. 

        7 months ago

        I was wondering if you can freeze the whole cake when finished? And if so, how long will it last? Will it get soggy when thawed?


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