Source: Martha Stewart Living, December/January 1998/1999
Yield Makes about 4 3/4 pounds
4 cups (8 sticks) unsalted butter, room temperature
1 teaspoon pure vanilla extract
3 cups confectioners' sugar
7 1/2 cups bread flour
1/3 cup Dutch process cocoa powder
To make the white dough, place 2 cups (4 sticks) butter, 1/2 teaspoon vanilla, 1 1/2 cups sugar, and 3 3/4 cups flour in the bowl of an electric mixer fitted with a paddle attachment. Mix on medium speed until well combined. Wrap the dough in plastic.
To make the black dough, combine, in the same bowl, the remaining 2 cups (4 sticks) butter, 1/2 teaspoon vanilla, 1 1/2 cups sugar, 3 3/4 cups flour, and the cocoa powder. Mix on medium speed until well combined. Wrap the dough in plastic. Store dough in the refrigerator up to 2 weeks or freeze up to 3 months.