Chocolate-Chocolate Birthday Cake

INGREDIENTS

2 sticks

unsalted butter, at room temperature (plus more for the pan)

2/3 cup

unsweetened cocoa powder (plus more for the pan)

2 cups

all-purpose flour

1 1/2 tsp

baking powder

1/2 tsp

baking soda

1/2 tsp

fine sea salt

1 1/4 cups

sugar

large eggs, at room temperature

2 tsp

pure vanilla extract

1 cup

buttermilk, well shaken

4 oz

bittersweet chocolate, melted and cooled

3 1/3 cups

confectioners’ sugar

4 1/2 tbsp

unsweetened cocoa powder

1/2 tsp

fine sea salt

3 sticks

unsalted butter, at room temperature

6 oz

bittersweet chocolate, melted and cooled

4 1/2 tbsp

buttermilk

Small decorations to scatter over the cake, optional