Chocolate Cake: Adjust oven rack to middle position and preheat oven to 350°F. Spray two 8-inch round cake pans with baking spray. Set aside.

In a stand mixer, stir the sugar, flour, cocoa, baking powder, baking soda, and salt together on low speed for 30 seconds.

Add the eggs, buttermilk, oil, and vanilla; increase speed to medium and beat for 2 minutes.

Reduce speed to the lowest and slowly add the boiling water. Stir on low for 1 minute.

Pour the batter into prepared pans and bake for 25-35 minutes or until a toothpick inserted comes out clean. Cool for 10 minutes, then remove from pans and cool completely.

Frost with Chocolate Frosting.

Chocolate Frosting: In a saucepan over medium heat, whisk the sugar, flour, cornstarch, salt, and cocoa together.

Slowly add milk while whisking briskly. Cook, whisking constantly until mixture boils.

Reduce heat and cook until thick, about 4-8 minutes. Transfer to a bowl, cover with plastic wrap, and cool for 2 hours.

In a stand mixer, beat butter until fluffy. Add cooled mixture and vanilla, beat until incorporated.

Add melted chocolate and beat until incorporated.