Best-Ever Chocolate & Nutella Layer Cake

INGREDIENTS

2 1/4 cups

all-purpose flour

2 1/3 cups

superfine sugar

3/4 cup

dark Dutch-process cocoa powder (I use Cacao Barry Extra Brute)

2 1/2 tsp

baking soda

2 tsp

baking powder

1 tsp

salt

1 1/4 cups

buttermilk

3/4 cup

brewed coffee or espresso

2/3 cup

vegetable oil

eggs, room temperature

1 tbsp

pure vanilla extract

4 1/2 cups

confectioners' sugar

1 1/2 cups

unsalted butter, room temperature

1 cup

Nutella (or other hazelnut spread)

3/4 cup

full-fat sour cream

11 oz

best-quality dark chocolate, melted and cooled slightly

1 tbsp

pure vanilla extract

salt