Ultimate Chocolate Cake with Chocolate Buttercream Frosting

It's another birthday cake! This is for the individual who wants to be buried alive in chocolate. 

Recipe  

Cake (makes a 3-layer 9-inch cake)
2 sticks unsalted butter, at room temperature
2 cups  firmly packed dark brown sugar
2/3 cup  granulated sugar
4 large eggs
2 cups buttermilk
2 teaspoons vanilla extract
2 3/4 cups all-purpose flour
1 1/3 cups  cocoa
1/2 teaspoon baking soda
1 teaspoon baking powder
pinch of salt

Chocolate Buttercream Frosting
3 ounces unsweetened chocolate, melted and cooled
4 cups confectioners’ sugar (no need to sift)
2 sticks unsalted butter, at room temperature
2 tablespoons half-and-half or whole milk
1 teaspoon vanilla extract

Preheat to 350 degrees. 

Spray pans with cooking spray, dust with flour, and line with parchment paper. 

Beat butter and sugars together until fluffy. 

Add in eggs 1 at a time.

Add in buttermilk and vanilla extract.

In separate bowl, mix flour, cocoa, baking soda, baking powder together, and salt. 

Slowly add dry to wet ingredients. 

Bake 20-25 minutes. 

For frosting:

Beat butter and confectioners' sugar together. 

Add in melted chocolate, milk, and vanilla extract slowly. 
For a thicker frosting, add in 1/2 cup confectioners' sugar.