Preheat the oven to 350°F. Grease and flour two 8-inch round cake pans and line the bottoms with parchment paper.

To make the cake, sift together flour, baking powder, and salt. In a separate bowl, beat the eggs and sugar with a mixer on high speed for 5-7 minutes until thick and pale. Gently fold in the flour mixture. In a small saucepan, heat the milk and butter just until the butter melts, then stir in the vanilla. Gradually add this to the batter and fold until incorporated.

Divide the batter evenly between the prepared pans and bake for 20-22 minutes or until a toothpick comes out clean. Cool in the pans for 10 minutes, then transfer to wire racks to cool completely.

To make the pastry cream, heat milk in a saucepan until just steaming. In a bowl, whisk sugar, cornstarch, and egg yolks. Slowly pour the hot milk into the egg mixture while whisking, then return the mixture to the saucepan. Cook over medium heat, whisking constantly, until thickened. Remove from heat, stir in butter and vanilla, then transfer to a bowl and cover with plastic wrap directly on the surface. Chill for at least 2 hours.

To make the ganache, heat cream until it begins to simmer. Pour over chopped chocolate and let sit for 2 minutes, then stir until smooth. Add corn syrup if using. Let cool slightly until it thickens to a pourable consistency.

To assemble, place one cake layer on a serving plate. Spread the chilled pastry cream evenly on top. Place the second cake layer over the cream. Pour the ganache over the top, letting it drip slightly down the sides.

Refrigerate for at least 1 hour before serving to set.