Directions-
Heat the oven to 350°. Grease and flour two 9-inch round pans and set them aside. In a microwave-safe liquid measuring cup, measure 1 1/2 cups water. Add the unsweetened chocolate squares to the water. Microwave for 2 to 3 minutes, stirring after 1 1/2 minutes or until the chocolate has melted. Stir in the cocoa and set the mixture aside.
In a large mixing bowl, cream the butter for 1 minute; add the granulated and brown sugars and cream for another 2 minutes or until light and fluffy. Add the eggs individually, beating well after each one. Beat in the vanilla extract.
In a separate bowl, stir together the flour, baking soda, and salt. Beginning with about a third of the flour, add the flour mixture and chocolate mixture alternately to the butter and sugar, stirring well after each addition.
Divide the cake batter evenly between the two pans, scraping the bowl with a rubber spatula. Place the pans on the middle oven rack and bake for 25 to 30 minutes or until a toothpick inserted in the middle of the cakes comes out clean.
Let the cakes cool in the pans for about 10 minutes. Then place a cooling rack atop each pan and, holding the edges to the pan, flip the cake onto the rack. Cool completely before frosting.
Place one layer on a plate and spread the top with chocolate frosting. Place the second layer on top and then frost the top and sides of the cake.
For a finishing touch, decorate the top and bottom edges of the cake with a piped icing border. Serves 8 to 10.