Preheat your oven to 350°F (175°C). In a large bowl, mix together the all-purpose flour, baking powder, and salt. In a separate bowl, whisk the eggs, milk, and vanilla extract until smooth. Gradually add the wet ingredients to the dry mixture, stirring until just combined. Pour the batter into prepared cake pans and bake for 25-30 minutes, or until the cakes are golden and a toothpick inserted in the center comes out clean. Allow them to cool completely.

While the cakes are cooling, prepare the vanilla custard. In a saucepan, heat the milk over medium heat until it begins to steam, but do not let it boil. In a separate bowl, whisk together the egg yolks, granulated sugar, and cornstarch until pale and well combined. Slowly pour the hot milk into the egg mixture, whisking continuously to prevent curdling. Return the mixture to the saucepan and cook over medium heat, stirring constantly, until it thickens to a pudding-like consistency. Set aside to cool slightly.

To make the chocolate ganache, heat the heavy cream in a small saucepan over medium heat until it starts to bubble gently. Remove it from the heat and pour it over the chopped semi-sweet chocolate in a bowl. Let it sit for about one minute to soften the chocolate, then stir until the mixture is completely smooth and glossy. Allow the ganache to cool slightly before using it.

Once the cake layers are completely cool, place one cake layer on a serving plate and generously spread the vanilla custard over the top. Carefully place the second layer of cake on top, pressing down gently. Finally, pour the smooth chocolate ganache over the entire pie, letting it drizzle down the sides for a lovely finish. Chill the assembled pie in the refrigerator for at least one hour before serving.