A classic is in a delicious sheet cake form! My Boston Cream Pie Sheet Cake starts with a soft yellow sheet cake, is slathered in a sweet pudding/custard, and topped off with gorgeous chocolate ganache rosettes.

I can’t believe we’re already on cake 9 of my 10-sheet cake series! To see all of them, make sure to search “sheet cakes” so that you never miss a new one! I have one more left after this, and it’s definitely my favorite, so stay tuned early next week.

I’ve always loved my Boston Cream Pie Cake from my Cake Confidence cookbook, but I had never turned it into a sheet cake before. I figured this one would be a fun addition to share with my sheet cake series. I’m so glad I did! It’s such a gorgeous cake, but is also one of the easier to make out of the sheet cake series.

Three parts, one cake

For our Boston Cream Pie Sheet Cake, I’ve chosen to use my yellow cake as a base, a vanilla custard/pudding as the filling, and then we’ve topped it all off with the chocolate ganache buttercream that dreams are made of! Each part is easy to make separately, and combined they make a gorgeous soft and creamy bite of cake. This cake truly is something special!

How to make a doctored yellow cake

Although you can have a white cake or vanilla cake be the base of this cake, I decided a yellow cake might be a tasty fit. You can use a white cake or vanilla cake mix instead of the yellow below and you will have similar results.

Here’s what you’ll need:

  • Buttermilk – I used room temperature. You can make your own with lemon juice or vinegar mixed with whole milk. Make sure to let it curdle before you use it so it has time to properly turn into buttermilk.
  • Sour Cream – I used full-fat sour cream, and make sure it’s room temperature.
  • Eggs – whole eggs and room temperature again. Notice a theme? 🙂
  • Vegetable oil – you only need 1/3 cup.
  • Vanilla – just a little will do.
  • Yellow Cake Mix – I used Duncan Hines, but you can use a similar brand for similar results. I do prefer the taste and texture of Duncan Hines, though.

The directions are below on how to combine these ingredients into a delicious cake batter.

What cake pan can I use?

I used this 9×13 pan, specifically. You can use a glass dish, or any baking dish, really.

Can I make this into cupcakes?

Yes! Just split the batter into 24 cupcakes, bake them up, hollow out the middle for the pudding/custard, and swirl a delicious ganache buttercream rosette on top.

Can I make my own pudding/custard or do I need to use the box mix?

You can certainly make your own from scratch. I chose to use a boxed vanilla custard/pudding filling, but if you prefer to make a homemade custard, I have a DELICIOUS scratch one in my I’ll Bring the Cake cookbook. For this version, though, yes, I opted for the boxed version. I know it’s not everyone’s cup of tea, but it’s a easy way to make a lot of yummy custard/pudding for the filling in no time. Just add milk to the mix (I used the jello brand mix for the vanilla bean pudding) and then spread it right onto the baked sheet cake. Before you add on any buttercream, make sure to place your custard-covered cake in the freezer for a couple minutes before you swirl on the chocolate rosettes.

Chocolate buttercream rosettes

It’s time to grab that Wilton 1M piping tip and make these gorgeous rosettes! You’re going to start with making a ganache and using the chocolate ganache right into the buttercream. Using good quality chocolate is key, and also making sure the ganache comes closer to room temperature before using it in your buttercream. For the rosettes, make sure to swirl the tail of the rosette under the next one so that it hides where one rosette ends and the next begins.

How to assemble the cake

Using an offset icing spatula, spread on the custard all over the surface of the baked and cooled cake.

Freeze the cake for 5 minutes to set the custard before swirling on the rosettes.

With the 1M piping tip, swirl on the buttercream in lined up rosettes. If you want to keep it simple, and aren’t in a rosette mood, just slather on the buttercream with a spoon, butter knife, or even your offset icing spatula in a rustic back and forth motion.

Here’s a quick video of the process:

If you make my cakes and bakes, I’d love to see it! Make sure to tag me @bakingwithblondie or #bakingwithblondie so I can join in on all the fun.

As always, Happy Baking!

xo, Mandy

Get the Recipe: Boston Cream Pie Sheet Cake

Tender yellow cake with a custard pudding filling, topped with chocolate ganache buttercream rosettes.
Servings: 20 servings, or less, depending on how you slice it
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Ingredients
 

Yellow Cake

  • 3/4 cup buttermilk, room temperature
  • 2/3 cup sour cream , room temperature
  • 3 whole eggs, room temperature
  • 1 egg white , room temperature
  • 1/3 cup vegetable oil
  • 1 Tablespoon vanilla
  • 1 15.25oz Yellow Cake Mix , I used Duncan Hines

Cream Filling

  • 1 5.1oz Box Vanilla Pudding Mix (or you can make homemade – I have a recipe for that in my "I'll Bring the Cake cookbook")
  • 3 cups whole milk

Chocolate Ganache Buttercream

  • 1 1/2 cups chocolate melts or chopped chocolate
  • 1 cup heavy cream
  • 1 cup (or two sticks) unsalted butter
  • pinch of salt
  • 1 Tablespoon vanilla
  • 1/4 cup cocoa powder
  • 6-7 cups powdered sugar

Equipment

  • 9×13 sheet pan/dish
  • Wilton 1M piping tip with piping bag
  • offset icing spatula

Instructions
 

For the cake

  • Preheat the oven to 325 degrees and prep a 9×13 sheet pan/dish with a swipe of shortening and dust of flour to prevent sticking (or you can use cooking spray, etc). Set aside.
  • In a large bowl, whisk together all the ingredients except for the cake mix. Sift in the cake mix, then gently to combine (don't overmix). Spread the cake batter into the prepared dish, then bake for 25-27 minutes. Let the cake cool completely before decorating.

For the pudding filling

  • While the cake is baking, make the filling. In a large bowl, whisk together the pudding mix and milk until it's thick. Refrigerate until the cake is cooled.

For the chocolate ganache buttercream

  • In a glass dish, microwave the chocolate + heavy cream for 30 seconds and stir. Heat 30 seconds again and stir until smooth. Let cool for 10-15 minutes.
  • In the bowl of a stand mixer fitted with a paddle attachment, whip up the butter until it's light and fluffy, then add in the cooled ganache, salt, vanilla, and cocoa powder until combined. Slowly add in the powdered sugar with the mixing speed on low, then increase the speed to the highest setting. Let the buttercream whip for 2 minutes until the texture and color lighten. *If you need to thin the texture, add in a 1/4 cup of heavy cream and mix again. Use a wooden spoon to beat out the air bubbles before adding the buttercream to your piping bag fitted with a wilton 1M piping tip.

Assembly

  • Spread on an even layer of the custard/pudding filling, then freeze for 5 minutes to set. Pipe on rosettes over the entire cake. There may be a little bit of buttercream left over, depending on how tight the rosettes are. If you don't want to pipe on buttercream swirls, use an offset icing spatula to spread on the buttercream in an even layer on top of the pudding layer. Serve within a couple days for max pudding freshness.
Author: Mandy Merriman, Baking with Blondie