01 - Preheat oven to 350°F. Grease and flour two 8-inch round cake pans or line with parchment paper.
02 - Sift together flour, baking powder, and salt in a bowl. Set aside.
03 - Beat eggs and sugar with electric mixer until pale and thick, about 5 minutes. Mix in vanilla.
04 - Gently fold flour mixture into egg mixture until just combined.
05 - Mix milk and melted butter together, then fold into batter until smooth.
06 - Divide batter evenly between prepared pans. Bake for 22–25 minutes until toothpick comes out clean. Cool in pans 10 minutes, then turn onto racks to cool completely.
07 - Heat milk in saucepan until just simmering.
08 - Whisk egg yolks, sugar, cornstarch, and salt in separate bowl. Slowly pour hot milk into yolk mixture while whisking constantly.
09 - Return mixture to saucepan and cook over medium heat, whisking constantly, until thick and bubbling, about 2–3 minutes. Remove from heat, whisk in butter and vanilla. Cover with plastic wrap touching surface and chill until cold.
10 - Place chopped chocolate and butter in bowl. Heat cream to simmer, pour over chocolate. Let sit 2 minutes, then stir until smooth.
11 - Place one cake layer on serving plate. Spread cooled pastry cream evenly over cake. Top with second layer.
12 - Pour chocolate ganache over top, allowing it to drip down sides. Chill at least 1 hour before serving.