Preheat your oven to 350°F (175°C). In a mixing bowl, whisk together the cake flour, baking powder, and salt.

In a separate bowl, cream together the unsalted butter and granulated sugar until light and fluffy, about 3–5 minutes.

Add in the room-temperature eggs one at a time, mixing well after each addition, then stir in the milk and vanilla extract.

Pour the batter into a greased 9-inch round cake pan and bake for 25–30 minutes or until a toothpick inserted comes out clean.

In a saucepan over medium heat, combine whole milk, granulated sugar, and egg yolks. Whisk in the cornstarch until no lumps remain.

Cook this mixture, stirring constantly, until it thickens and begins to bubble, about 5–7 minutes.

Once thickened, remove from heat, stir in the butter and vanilla extract until smooth. Set aside to cool slightly.

Once the cake has cooled completely, carefully slice it in half horizontally to create two layers.

Place the bottom layer on a serving plate and spread half of the vanilla custard over it evenly.

Gently place the top layer of the cake on the custard and spread the remaining custard on top.

In a small saucepan, heat heavy cream over medium heat until it begins to simmer.

Remove from heat and add the chopped semi-sweet chocolate. Let sit for a minute, then stir until smooth.

If desired, stir in 1 tablespoon of butter for added richness.

Carefully pour the chocolate glaze over the assembled Boston Cream Pie and let it drizzle down the sides.

Let the pie sit at room temperature for about 30 minutes to allow the glaze to set before slicing.

For the best flavor, refrigerate for a couple of hours before serving if you prefer it chilled.