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  • Writer's pictureSarah

Bake-Along #18: Boston Cream Pie Blondies

Updated: Nov 15, 2020

A brand new item created from your poll choices! For tips and to bake-along live, just follow along with the video.

Prep: 45 minutes

Bake: 15-20 minutes

Rest: 1 hour

Boston Cream Pie Blondies (and their inspirations!)

Blondie Base (replaces the vanilla cake):

  • 1 &1/2 cups light brown sugar

  • 3/4 cup unsalted butter

  • 1 egg

  • 1 egg yolk

  • 1 1/2 t vanilla extract

  • 1 1/2 cups all-purpose flour

  • 3/4 t salt

  • 1/2 cup semi-sweet chocolate chips

German Buttercream (Or "Custard Buttercream" replaces the vanilla pastry cream):

  • 2 cups milk

  • 4 t vanilla extract (divided)

  • 1/4 cup cornstarch

  • 2/3 cup granulated sugar

  • 2 egg yolks

  • 2 cups unsalted butter

  • 1/4 cup powdered sugar

  • 1/4 t salt

Chocolate Ganache (replaces the chocolate drizzle):

  • 1 & 1/2 cups chocolate (I'd recommend bittersweet if you can grab it!)

  • 3/4 cup heavy cream

  1. Pre-heat your oven to 350°F.

  2. First we'll make the custard: put your milk and 1 t vanilla extract (the rest will come later) in a sauce pan and heat until steaming.

  3. Whisk together your egg yolks, cornstarch, and granulated sugar. Add a few splashes of your milk mixture to thin it out and make it easier to whisk together.

  4. Once your milk is steaming, temper your egg mixture by pouring a few tablespoons of milk into your eggs, whisking the entire time. Do this until you've incorporated about a quarter cup.

  5. Pour the egg mixture into the saucepan and whisk over medium heat until it is thick. You can see my custard's consistency at the 12:13 mark.

  6. Pour your custard into a large dish. Press plastic wrap directly on top of custard so it doesn't form a skin. Put the dish of custard into the refrigerator or freezer. You are looking to bring it down to room temperature.

  7. Next we'll start on the blondies: prepare a 9" x 13" pan with grease or parchment paper.

  8. cream together the sugar and butter using the paddle attachment of your stand mixer.

  9. Add the eggs and vanilla extract, ensuring it is all thoroughly combined.

  10. Next add your flour and salt, a little at a time until incorporated.

  11. Beat in your chocolate chips just until combined. Spread in prepared pan.

  12. Bake for 15-20 minutes until the blondies are golden brown on top and are set (better to under bake than overbake these!). Check out my cooked blondies at the 50:47 mark.

  13. While those bake we can continue our buttercream: beat the 2 cups unsalted butter with your paddle attachment until it is light and fluffy.

  14. Pull your room temperature custard out of the fridge or freezer (or a combination, which is what I did in the video!). If your center is still warm, that's okay: give the custard a whisk to loosen it up and even out the temperature throughout. If you're wondering what I mean, here's a visual at the 39:10 mark.

  15. With the mixer running, incorporate your custard into the butter, about a tablespoon at a time. You want to allow the custard to fully incorporate before adding more.

  16. One it is all combined, sweeten your buttercream with the powdered sugar and flavor it with 1 T vanilla extract (feel free to do both of these to taste!)

  17. Switch to the whisk attachment and whip until the mixture is light and fluffy, about 3-4 minutes. My final buttercream is at the 51:02 mark.

  18. For the ganache: place the chocolate chips in a heat proof bowl.

  19. Heat the heavy cream over medium low heat until it is hot and steaming, but not boiling.

  20. Pour the heated cream over the chocolate chips and allow to rest for a minute or two. Then gently mix with a heat proof spatula until the chocolate chips are fully incorporated and the mixture is thick and glossy (and just plain gorgeous). Check out mine at the 57:52 mark.

  21. Now we assemble! (My sped up assembly is at the end! You can see it at the 59:33 mark. I refrigerated the buttercream layer before adding ganache).

  22. Make sure all of your pieces are at room temperature or colder.

  23. First layer your German buttercream onto the cooled blondies. I like to refrigerate these two together for 20 minutes before adding the ganache.

  24. Then I spread an even layer of ganache onto the slightly chilled buttercream.

  25. Refrigerate the enter pan until the ganache is set (this won't take too long!). Also you can eat this at any time, but it won't cut quite as cleanly.

  26. Here is the final product at 52:14!

  27. Then cut (or just eat it right out of the pan...) and enjoy!


  • Flavor the German buttercream to your heart's content! You can add in all sorts of different flavors like you would any other buttercream.

  • German buttercream isn't incredibly stable at room temperature for long period's of time, so for long term I would recommend covering these and storing them in the refrigerator.

  • If you like a thicker, thinner, or less or more ganache, go for it! Here we're using a 2:1 ratio of chocolate to cream. You can increase or decrease while using that ratio, or mix up the ratio for thinner ganache (more cream than chocolate).

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