In a small saucepot, stir to the cornstarch, salt, and sugar.

Whisk in the milk and egg yolks until combined.

Cook over medium-heat, stirring constantly until it boils.

Simmer for 1 minute before removing from the heat.

Pass through a sieve into bowl with chocolate, butter, and vanilla extract.

Stir until smooth, and cover with plastic wrap touching the surface of the pudding.

Chill for at least 4 hours.

Grease and line 2 9-inch cake pans, and preheat your oven to 350°F.

In a bowl, sift and mix together the dry ingredients.

In a separate bowl, cream together the butter and sugar until lightened.

Whisk in the eggs until fluffy.

Whisk in the sour cream, vanilla extract, and oil.

Fold in of the dry ingredients until barely incorporated.

Stir in the buttermilk until mixed.

Fold in the last of dry ingredients until combined.

Divide among the cake pans.

Bake for 30-35 minutes until a toothpick inserted into the cake comes out with moist crumbs.

Cool in the pans for 15 minutes before cooling completely on a wire rack.

In a bowl of stand mixer, add in egg whites, sugar, salt, and cream of tartar.

Place over a pot of simmering water, and whisk until the egg whites are warm, and the sugar is dissolved.

Whisk in the stand mixer on medium-high to high speed until stiff peaks form.

Add in the butter, a little at a time until it resembles "cottage cheese."

Switch to a paddle attachment, and beat on high-speed until smooth.

Mix in the vanilla extract, and melted chocolate until combined.

Set aside.

Trim the tops of the cake layers on a turntable.

Crumble the cake tops into small, uniform pieces, and set aside.

Pipe a frosting border around the edge of a cake layer.

Spread a generous amount of chocolate pudding within the border of the cake.

Place the 2nd cake layer, face down on top.

Spread a thin amount of frosting over the entire cake.

Chill for 30 minutes to set the frosting.

Spread the rest of the frosting over the entire cake.

Use a bench scraper to smooth the outside.

Coat the sides of the cake with the cake crumbs.

Keep at room temperature, or refrigerate, (serve at room temperature).

Slice into 10-12 slices.

Enjoy!