Make the Cake:

1. Preheat your oven to 350°F (175°C). Grease two 9-inch round cake pans, line the bottoms with parchment paper, then grease the parchment. Dust lightly with flour and tap out excess.
2. In a medium bowl, whisk together flour, baking powder, and salt. Set aside.
3. In a large bowl using an electric mixer, beat the eggs and sugar on high speed for 5-7 minutes until the mixture is thick, pale yellow, and tripled in volume. When you lift the beaters, the mixture should fall in ribbons that hold their shape briefly on the surface.
4. In a small saucepan or microwave, warm the milk and melted butter together until just warm (not hot). Stir in vanilla extract.
5. Gently fold the flour mixture into the egg mixture in three additions using a rubber spatula. Use a folding motion (cut down the center, sweep along the bottom, and bring up the sides) to preserve the air you’ve beaten into the eggs. Mix just until no flour streaks remain.
6. Take about 1 cup of the batter and fold it into the warm milk-butter mixture to temper it, then gently fold this mixture back into the main batter. Work quickly but gently.
7. Divide the batter evenly between the prepared pans. Bake for 22-25 minutes until the cakes are golden, spring back when lightly pressed, and a toothpick inserted in the center comes out clean.
8. Cool in pans for 10 minutes, then turn out onto wire racks, peel off parchment, and cool completely.

Make the Pastry Cream:

9. In a medium saucepan, heat the milk and ¼ cup of sugar over medium heat until steaming and sugar dissolves. Don’t let it boil.
10. Meanwhile, in a bowl, whisk together egg yolks, remaining ¼ cup sugar, and cornstarch until smooth and pale.
11. Slowly pour about half of the hot milk into the egg mixture while whisking constantly (this tempers the eggs and prevents scrambling). Then pour the egg mixture back into the saucepan with the remaining milk.
12. Cook over medium heat, whisking constantly, until the mixture thickens and comes to a boil. Let it boil for 1 minute while whisking (this cooks out the starchy taste).
13. Remove from heat and whisk in butter and vanilla until smooth. Pour through a fine-mesh strainer into a clean bowl to remove any lumps.
14. Press plastic wrap directly onto the surface of the custard (this prevents a skin from forming) and refrigerate until completely cold, at least 2 hours or overnight.
15. Optional: When ready to assemble, whip the heavy cream to soft peaks and fold it into the cold pastry cream for a lighter, fluffier filling.

Make the Chocolate Ganache:

16. Place chopped chocolate in a heat-proof bowl. Heat the cream in a small saucepan until it just begins to simmer (don’t boil).
17. Pour hot cream over the chocolate and let sit for 1 minute undisturbed. Then whisk until completely smooth and glossy. Stir in corn syrup if using. Let cool for 10-15 minutes until slightly thickened but still pourable.

Assemble the Boston Cream Pie:

18. If your cake layers have domed tops, use a serrated knife to level them. Place one cake layer on your serving plate or cake stand, cut side up.
19. Spread the chilled pastry cream evenly over the bottom cake layer, leaving a ½-inch border around the edges (the weight of the top layer will push it out slightly).
20. Place the second cake layer on top, cut side down, pressing gently to adhere.
21. Pour the ganache over the top of the cake, starting in the center and using an offset spatula to spread it to the edges, letting it drip naturally down the sides if desired.
22. Refrigerate for at least 30 minutes to set the ganache before slicing. Serve chilled or at room temperature.