Preheat your oven to 350°F (175°C). In a large mixing bowl, whisk together the all-purpose flour, baking powder, and salt. In another bowl, beat the eggs, milk, vanilla extract, and granulated sugar until well combined. Gradually fold the dry ingredients into the wet ingredients until just blended, ensuring no lumps remain. Pour the luscious batter evenly into two greased cake pans.

Place the cake pans in the preheated oven and bake for 25-30 minutes. You'll know it's ready when the tops are golden brown, and a toothpick inserted into the center comes out clean. Once baked, carefully remove the pans from the oven and let them cool on a wire rack for about 10 minutes before gently removing the cakes from the pans to cool completely.

In a saucepan, heat the milk over medium heat until it just begins to bubble. While the milk warms, whisk the egg yolks and granulated sugar together in a separate bowl until the mixture becomes pale and creamy. Slowly pour the hot milk into the egg yolk mixture, whisking constantly to temper the eggs. Return the mixture to the saucepan and cook over low heat, stirring continuously until it thickens, about 5-7 minutes. Allow the custard to cool to room temperature.

In a small saucepan, heat the heavy cream over medium heat until it begins to simmer. Remove it from the heat and immediately pour it over the chopped chocolate in a mixing bowl. Let it sit for one minute to melt the chocolate, then stir it gently until you achieve a smooth and glossy ganache. Allow it to cool slightly before using.

On a serving plate, place one layer of cake and spread the cooled custard filling generously over the top. Carefully place the second cake layer on top, creating a delightful sandwich. Finally, pour the rich chocolate ganache over the entire cake, ensuring an even coating. Chill the assembled Boston Cream Pie in the refrigerator for at least two hours to let the flavors meld and set beautifully.