Preheat your oven to 350°F (175°C) and grease two 9-inch round cake pans. Line the bottoms with parchment paper.

In a large mixing bowl, cream together softened unsalted butter and granulated sugar until light and fluffy, about 3-5 minutes. Add eggs one by one, mixing well after each addition along with the vanilla extract.

In a separate bowl, sift together the cake flour and baking powder. Gradually stir the dry mixture into the creamed butter mixture, alternating with the milk, until just combined.

Pour the cake batter evenly into prepared pans and bake for 25–30 minutes, or until a toothpick comes out clean.

In a medium saucepan, combine milk, egg yolks, sugar, and cornstarch. Whisk continuously over medium heat until thickened and bubbling, about 8–10 minutes. Stir in vanilla extract, cover to cool.

In a small saucepan, heat heavy cream until it simmers, then remove from heat and add chopped chocolate, stirring until smooth and glossy.

Once cakes and custard are cool, slice each cake layer in half to create four layers. Layer custard between cakes and pour chocolate glaze over the top.

Refrigerate for at least 1 hour before serving to allow custard to set.