Preheat your oven to 350°F (175°C). Grease and line six 8-inch cake pans with parchment paper. If you don’t have six pans, bake in batches.

In a medium bowl, whisk together the cake flour, baking powder, and salt. Set aside.

In a large mixing bowl, beat the butter and sugar together on medium speed until light and fluffy (about 3-4 minutes).

Add the eggs, one at a time, beating well after each addition. Stir in the vanilla extract.

Reduce the mixer speed to low and alternate adding the flour mixture and milk, beginning and ending with the flour. Mix just until combined. Overmixing can lead to a dense cake.

Divide the batter evenly among the cake pans. Smooth the tops with a spatula.

Bake for 12-15 minutes or until a toothpick inserted into the center comes out clean.

Let the cakes cool in the pans for 10 minutes, then transfer them to a wire rack to cool completely.

In a saucepan, heat the milk over medium heat until it begins to steam (do not boil).

In a separate bowl, whisk together the sugar, cornstarch, and egg yolks until smooth.

Gradually pour about ½ cup of the hot milk into the egg mixture, whisking constantly to temper the eggs.

Pour the egg mixture back into the saucepan and cook over medium heat, whisking continuously, until the custard thickens (about 5 minutes).

Remove from heat and stir in the butter and vanilla extract.

Transfer the custard to a bowl, cover with plastic wrap (press it directly onto the surface to prevent a skin from forming), and refrigerate for at least 2 hours.

Place one cake layer on a serving plate. Spread a thin layer of custard filling evenly over the top.

Repeat with the remaining cake layers and custard, ending with the final cake layer on top.

Refrigerate the assembled cake for at least 1 hour to set before adding the ganache.

Heat the heavy cream in a small saucepan over medium heat until it just begins to simmer.

Remove from heat and pour over the chopped chocolate. Let sit for 2-3 minutes before whisking until smooth.

Stir in the butter for added shine. Let the ganache cool slightly until it thickens but is still pourable.

Pour the ganache over the chilled cake, using a spatula to help it flow evenly over the sides.

Let the ganache set at room temperature for 30 minutes, then refrigerate for at least 1 hour before slicing.