Preheat oven to 350°F (175°C). Grease and flour two round cake pans.

In a bowl, mix cake flour, sugar, baking powder, and salt.

In another bowl, cream softened butter and sugar until light and fluffy. Add eggs one at a time, mixing well after each addition. Gradually add milk until combined.

Combine dry ingredients with wet mixture gently until just incorporated.

Divide the batter between prepared pans and bake for 25-30 minutes or until a toothpick comes out clean. Let cool completely.

For the custard filling, whisk heavy cream, cornstarch, sugar, egg yolks, and vanilla in a saucepan over medium heat until thickened. Allow to cool before spreading between cake layers.

To make the ganache, melt dark chocolate chips with heavy cream over low heat until smooth; let cool slightly before drizzling over the assembled cake.