INGREDIENTS
1/2 cup
plus 1 tablespoon Dutch-process cocoa powder
1/2 cup
plus 1 tablespoon hot water
2 1/4 cups
all-purpose flour
3/4 tsp
baking soda
3/4 tsp
baking powder
1/2 tsp
salt
2 sticks
plus 1 tablespoon unsalted butter, at room temperature
1 2/3 cups
sugar
3
large eggs, at room temperature
1 tbsp
vanilla extract
3/4 cup
sour cream
1 cup
(8 oz.) unsalted butter, at room temperature
2 cups
confectioners’ sugar, sifted
salt
1
vanilla bean, split lengthwise (optional)
4 tsp
heavy cream
2 tsp
vanilla extract
3/4 cup
heavy cream
1/4 cup
light corn syrup
8 oz
bittersweet chocolate, finely chopped
1/2 tsp
vanilla extract