Don't be intimidated by the steps in this recipe. It looks like a lot but boils down to forming an assembly line. You can make the cupcake part the day ahead, or even freeze them for a few weeks, but wait to add the pastry cream and chocolate until a few hours before you want to serve. If you have to transport them, set aside some extra time for the chocolate to fully set.
And incidentally, if you're craving Boston Cream Pie in its full-on cake form, just double everything in this recipe. Bake the cake in two 9" cake pans, sandwich them with pastry cream, and pour the chocolate ganache over top.
Boston Cream Cupcakes
Makes 12 cupcakes
For the cupcakes:
1 1/2 cups (7 1/2 oz) cake flour
1 1/2 teaspoon baking powder
1/2 teaspoon salt
1/4 teaspoon baking soda
1/2 cup (4 oz) unsalted butter, softened
1 cup (8 oz) white sugar
2 large eggs
1 teaspoon vanilla extract
2/3 cup (5 1/2 oz) buttermilk
For the pastry cream filling:
1/4 cup (2 oz) white sugar
2 tablespoons all-purpose flour
1/4 teaspoon salt
2 large egg yolks
2/3 cup (5 1/2 oz) whole milk
1/2 teaspoon vanilla extract
For the chocolate ganache:
1 cup (6 oz) semi-sweet chocolate chips
1/3 cup (3 oz) heavy cream
To make the cupcakes:
Heat the oven to 375°F. Line a 12-cup muffin tin with cupcake liners. Spray the top of the muffin top with non-stick coating.
Sift together the cake flour, baking powder, salt, and baking soda. Set aside.
With a standing mixer fit with a paddle attachment or with a handheld mixer, cream the butter and sugar on high speed until they turn light yellow and look like frosting. Scrape down the sides of the bowl and beat in the eggs one at a time, scraping down the sides of the bowl as needed. Beat in the vanilla.
With the mixer on medium-low speed, beat in 1/3 of the flour until the flour is just barely combine. Beat in half of the buttermilk. Continue alternating between the flour and the buttermilk, ending with the last of the flour.
Divide the batter between the cupcake liners. Bake for 20-22 minutes, until the cupcakes are domed and beginning to turn golden. Let them cool in the muffin tin for a few minutes, then turn them out onto a wire rack. Make sure the cupcakes are completely cool before assembling.
To make the pastry cream:
Have a strainer over a heat-proof bowl standing ready near the stove.
Whisk together the sugar, flour, and salt in a small bowl. Whisk in the egg yolks to form a sticky paste.
Warm the milk in a small sauce pan just until you see it beginning to steam. Remove it from heat and pour a little into the egg mixture. Quickly whisk the eggs to thin out the paste. When you see no more lumps, slowly pour the rest of the milk into the eggs while continuing to whisk.
Pour the milk and egg mixture back into the saucepan and set over medium heat. Whisk constantly. At first, the mixture will feel very loose and liquidy, but it will start to thicken in a few minutes. It's important to keep whisking so the eggs on don't cook. When the pastry cream has thickened to the consistency of pudding, stop whisking and check for bubbles. If you see large bubbles plopping on the surface, the pastry cream is done.
Remove the pan from heat and whisk in the vanilla. Pour the pastry cream through the strainer set over the bowl, stirring until it has all fallen through. The strainer will catch any eggs that started to curdle. Press a piece of plastic wrap or wax paper directly to the surface of the pastry cream and refrigerate until completely chilled.
To assemble the cupcakes:
Use a paring knife to cut cones from the center of each cupcake. Angle your knife toward the center of the cupcake and cut a quarter-sized circle. Fill the hole with a tablespoon or two of cooled pastry cream.
To make the ganache, set the chocolate in a heat-proof bowl. Warm the milk until it's steaming and pour it over the chocolate. Let this stand for a minute, then mix until they form a thick, glossy paste. Pour a generous spoonful of ganache over each cupcake, spreading it with the back of the spoon to even out the top.
The cupcakes can be eaten immediately while the ganache is still warm, or you can wait an hour or two until the ganache has set (if the weather is hot or humid, place the cupcakes in the fridge until the chocolate is set). Once the ganache is set, the cupcakes can be served with less mess or packed for transport elsewhere.