Preheat oven to 350 degrees.
Line two 12-cup muffin tins with cupcake papers. Set aside.
In a small bowl, sift together the flour and baking soda. Set aside.
In a large bowl, on the medium speed of an electric mixer, cream the butter until smooth. Add the sugars and beat until fluffy, about 3 minutes. Add the eggs, one at a time, beating well after each addition. Add the chocolate, mixing until well incorporated. Add the dry ingredients in three parts, alternating with the buttermilk and vanilla. With each addition, beat until the ingredients are incorporated, but do not overbeat. Using a rubber spatula, scrape down the batter in the bowl to make sure the ingredients are well blended and the batter is smooth. Carefully spoon the batter into the cupcake liners, filling them about three-quarters full. Bake for 20–25 minutes, or until a cake tester inserted in the center of the cupcake comes out clean.
Cool the cupcakes in the tins for 15 minutes. Remove from the tins and cool completely on a wire rack before icing. At the bakery we ice the cupcakes with either Vanilla Buttercream or Chocolate Buttercream.
Note: If you would like to make a layer cake instead of cupcakes, divide the batter between two 9-inch round cake pans and bake the layers for 30–40 minutes.
Source: http://www.recipelink.com/cookbooks/2005/0743246616_3.html Chocolate Buttercream INGREDIENTS 2 9-inch cakes or 2 dozen cupcakes 1 1/2 cups unsalted butter, softened 2 tablespoons milk 9 ounces semisweet chocolate, melted and cooled to lukewarm 1 teaspoon vanilla extract 2 1/4 cups sifted powdered sugar DIRECTIONS 1. Note: to melt the chocolate, place in a double boiler over simmering water on low heat for 5-10 minutes; stir occasionally until the chocolate is completely smooth and no pieces remain; remove from heat and let cool 5-15 minutes or until lukewarm.
To make the buttercream: In a large mixing bowl, beat the butter using an electric mixer on MEDIUM speed for about 3 minutes or until creamy.
Add the milk carefully and beat until smooth.
Add the melted chocolate and beat well for 2 minutes.
Add the vanilla and beat for 3 minutes.
Gradually add in the sugar and beat on LOW speed until creamy and of desired consistency.
**For icing a 3-layer cake use the following measurements: 2 cups unsalted butter, 3 tablespoons milk, 12 ounces semisweet chocolate, 1 1/2 teaspoons vanilla extract, 3 cups sifted powdered sugar.