Mint chocolate cake Recipe

Name: Mint chocolate cake Recipe
Ingredients: 1 cup (2 sticks) butter, at room temperature, plus more for greasing the pans; 2 cups (8 1/2 ounces) flour, divided; 3/4 cup Dutch-process cocoa; 1 cup boiling water; 1 1/2 cups sugar; 3 eggs; 2 teaspoons vanilla; 1 tablespoon baking powder; 3/4 teaspoon salt; 1 1/4 cups (2 1/2 sticks) butter, at room temperature; 2 1/2 (1-pound) boxes confectioner's sugar, sifted; Heaping 1/2 teaspoon salt; Scant 2 teaspoons peppermint extract; 1/4 to 1/2 cup milk, or to taste; Prepared cake layers (see related recipe)