Double Chocolate Frosting | La Cucina Grandinetti

Ingredients

• 1/4 cup plus 2 tablespoons unsweetened Dutch-process cocoa powder
• 1/4 cup plus 2 tablespoons boiling water
• 1-1/2 cups (3 sticks) unsalted butter, room temperature
• 1 pound confectioners' sugar, sifted
• pinch of salt
• 1 pound best-quality semisweet chocolate, melted and cooled
• 2 teaspoons vanilla