1. Make the Vanilla Pastry Cream

The first step in preparing your Boston Cream Pie is making the vanilla pastry cream, as it needs time to chill and set before being used in the cake.

• Heat the milk: Pour the milk into a medium saucepan and place it over medium heat. Heat the milk until it just begins to simmer, then remove it from the heat immediately to avoid scorching.
• Whisk the egg yolks and sugar: In a separate large bowl, whisk together the egg yolks and sugar. The goal is to combine these ingredients until they become light in color and thick in texture.
• Add the cornstarch: Sift the cornstarch into the egg mixture and whisk vigorously until smooth.
• Temper the eggs: Gradually whisk in about ¼ cup of the hot milk mixture into the egg mixture to temper the yolks. This prevents the eggs from curdling when combined with the hot milk. Once tempered, slowly incorporate the rest of the hot milk.
• Strain and cook: Strain the combined mixture back into the saucepan through a fine-mesh sieve to remove any lumps. Return the saucepan to medium-high heat and cook, whisking constantly, until the mixture thickens and reaches a slow boil.
• Finish the cream: After thickening, continue to whisk for 1-2 minutes, then remove the saucepan from the heat. Stir in the butter until fully incorporated. Cover the pastry cream with plastic wrap, ensuring it touches the surface to prevent a skin from forming, and refrigerate it until fully chilled.

2. Make the Vanilla Sponge Cake

Next, you’ll prepare the vanilla sponge cake, which forms the base of your Boston Cream Pie.

• Preheat the oven: Preheat your oven to 350°F (175°C). Grease and flour an 8-inch round cake pan.
• Mix the wet ingredients: In a medium saucepan, melt the butter with the milk over low heat. Once melted, remove the saucepan from the heat and allow it to cool slightly. In a separate bowl, whisk together the eggs and sugar until light and fluffy. Add the cooled milk and butter mixture, followed by the vanilla extract.
• Combine the dry ingredients: In another bowl, sift together the flour, baking powder, and salt.
• Combine wet and dry ingredients: Gradually fold the dry ingredients into the wet mixture, being careful not to deflate the batter. The result should be a smooth, light batter.
• Bake the cake: Pour the batter into the prepared cake pan and smooth the top. Bake for 30-33 minutes, or until a toothpick inserted into the center comes out clean.
• Cool the cake: Allow the cake to cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely.

3. Make the Chocolate Ganache

While the cake is cooling and the pastry cream is chilling, you can prepare the chocolate ganache.

• Heat the cream: Pour the heavy whipping cream into a small saucepan and heat it over medium heat until it begins to simmer. Remove from heat as soon as it starts to bubble.
• Add the chocolate: Place the chopped bittersweet chocolate in a heatproof bowl and pour the hot cream over it. Let it sit for a minute to melt the chocolate, then stir until smooth and glossy.
• Let it cool: Allow the ganache to cool to room temperature, stirring occasionally to ensure it doesn’t harden too quickly.

4. Assemble the Boston Cream Pie

Now comes the fun part—putting everything together!

• Layer the cake: Slice the cooled sponge cake in half horizontally to create two layers.
• Fill with pastry cream: Spread a generous amount of chilled pastry cream over the bottom layer of the cake. Be sure to spread it evenly, leaving a small border around the edges.
• Top with the second layer: Place the second layer of sponge cake on top of the pastry cream.
• Drizzle with ganache: Pour the cooled chocolate ganache over the top layer of cake, allowing it to flow down the sides.
• Chill and serve: Refrigerate the assembled cake for at least 1 hour to allow the ganache to set. Once chilled, slice and serve!