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Mocha Hazelnut Boston Cream Pie

This twist on the classic Boston Cream Pie uses toasty hazelnuts, bittersweet espresso, and dark chocolate to create a perfectly balanced cake. Fluffy and soft hazelnut and coffee cake is filled with a layer of smooth espresso pastry cream and crunchy hazelnuts, and topped with a glossy dark chocolate ganache. This recipe is perfect for any get together where you want to show off your skills!
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Prep Time 4 hours
Cook Time 30 minutes
Total Time 6 hours
Servings: 12 slices
Ingredients Method

Ingredients
  

Espresso Pastry Cream
  • 2 cups half and half
  • 2 Tablespoons espresso powder
  • 6 large egg yolks at room temperature
  • ½ cup granulated sugar
  • a pinch of salt
  • ¼ cup all purpose flour
  • ¼ cup unsalted butter cut into four pieces
  • 1 teaspoon vanilla bean paste or extract.
Espresso Hazelnut Cake
  • 1 cup raw unsalted hazelnuts
  • 1 ¾ cup cake flour
  • ¾ teaspoon baking powder
  • ¼ teaspoon baking soda
  • 1 teaspoon espresso powder
  • 1 Tablespoon cocoa powder
  • ¼ teaspoon salt
  • ½ cup unsalted butter softened to room temperature
  • ¾ cup granulated sugar
  • ¼ cup Nutella
  • 3 large egg whites at room temperature
  • 2 teaspoons vanilla extract
  • ½ cup sour cream at room temperature
  • ½ cup whole milk at room temperature
  • ⅓ cup brewed coffee at room temperature
Topping
  • ⅓ cup chopped hazelnuts plus more for topping
  • ½ cup + 1 Tablespoon heavy cream
  • 4 ounces bittersweet chocolate coarsely chopped

Method
 

Make the pastry cream
  1. In a large saucepan, whisk the half and half and espresso powder together over medium heat until simmering. While it heats up, whisk together the egg yolks, sugar, and salt in a medium bowl. Whisk in the flour, the mixture will be thick. Stirring constantly, slowly pour ½ cup of the simmering half and half into the egg yolk mixture. Then, whisking constantly, slowly pour the egg yolk mixture back into the remaining simmering cream and lower the temperature to medium low.
  2. Cook, stirring constantly for 7 minutes until very thick. It will begin thickening very quickly, but let it keep cooking. Turn the heat back up to medium and cook, stirring vigorously for 1-2 minutes until very thick. It will be boiling at this point. Remove from the heat and add the butter, then whisk vigorously to combine and avoid splitting. Pour the mixture through a sieve to remove any lumps of cooked egg (this might be a little difficult because it is so thick). Finally, stir in the vanilla extract. Cover the mixture with cling wrap, making sure it is touching the surface of the cream to prevent a skin from forming, and chill in the fridge for 2 hours. It will thicken even more as it chills. 
Prepare the hazelnuts
  1. Preheat the oven to 300℉. Line a small baking sheet with parchment paper. Spread the hazelnuts on the sheet evenly. Bake for 5-10 minutes or until they are lightly toasted. Remove from the oven and increase the temperature to 350℉. Allow the toasted nuts to cool for 5-10 minutes.
  2. Add the toasted hazelnuts to a food processor and pulse until they resemble a fine meal, similar to almond flour. Set aside. 
Make the cake
  1. Grease the bottom and sides of two 8 inch cake pans, then line the bottoms with parchment paper rounds, and finally grease the parchment. Preheat the oven to 350℉.
  2. In a medium bowl, whisk together 3/4 cup of the ground toasted hazelnuts(you should have some extra), flour, baking powder, baking soda, espresso powder, cocoa powder, and salt. Set aside.
  3. In a large bowl using either a stand or hand mixer fitted with a paddle attachment, beat the butter on medium speed until smooth, around 1 minute. Add the granulated sugar and beat until fluffy and creamy, about two minutes. Add the Nutella and beat until combined. Scrape down the sides and bottom of the bowl with a rubber spatula as needed. Add the egg whites and vanilla and beat until creamy. Mix in the sour cream.
  4. With the mixer running on low speed add the dry ingredients to the wet ingredients and beat until just combined. Slowly stream the milk into the batter with the mixer still running on low. Do the same with the brewed coffee. 
  5. Spoon/pour the batter evenly among each prepared cake pan.
  6. Bake the cupcakes for 19-22 minutes or until an inserted toothpick comes out clean, and the cake is pulling away from the sides of the pan. Let the cakes cool completely in the pan set on a wire cooling rack.
Assemble
  1. Remove the cooled cakes from the pans and place one layer on a cake stand and spread a very thick layer of pastry cream on top. You may not use all of the pastry cream, but it should be a pretty thick layer. Top the custard with ½ cup of chopped hazelnuts. Place the other cake layer on top and set the cake in the fridge while we make the ganache.
Make the ganache
  1. Place the chopped chocolate in a medium sized liquid measuring cup. Heat the heavy cream in a small saucepan until simmering. Pour the warm cream over the chopped chocolate and let the mixture sit unbothered for 3-5 minutes to soften the chocolate. Then, slowly and carefully stir until the ganache is smooth and glossy.
  2. Remove the cake from the fridge and pour the ganache on top, letting it drip down the sides. Don't pour all of it at once, you may not end up using it all. Top with any remaining chopped hazelnuts. Let the ganache set in the fridge for about 10 minutes before slicing and serving
  3. Cake stays fresh sealed tightly in the refrigerator for up to 3 days.