Double-Chocolate Espresso Cake

Name: Double-Chocolate Espresso Cake
Prep time: 1 h
Total time: 1 h
Cuisine: European
Ingredients: 2 cups all-purpose flour; 3/4 cup unsweetened cocoa powder; 1 1/2 tsp baking soda; 1 tsp baking powder; 1/2 tsp salt; 3/4 cup unsalted butter , at room temperature; 3/4 cup granulated sugar; 3/4 cup lightly packed brown sugar; 2 eggs; 2 tsp vanilla; 1 1/2 cups buttermilk; 1 cup unsalted butter , at room temperature; 225-g pkg unsweetened chocolate , chopped and melted; 1 tbsp vanilla; 1/4 tsp salt; 6 cups icing sugar , sifted; 1/2 cup milk; 1/4 cup espresso , or strong coffee