INGREDIENTS
1/2 cup
unsweetened cocoa powder, sifted
1/2 cup
(packed) dark brown sugar
1 cup
boiling water
9 tbsp
unsalted butter, softened, plus more for greasing
3/4 cup
sugar
1 1/2 cups
all-purpose flour
1/2 tsp
baking powder
1/2 tsp
baking soda
2 tsp
vanilla extract
2
eggs
1 1/4 cups
sugar
1/3 cup
water
3
large egg whites
1/4 tsp
cream of tartar or 1 tablespoon light corn syrup
1 tsp
vanilla extract