4 ounces (120 grams) unsweetened chocolate, coarsely chopped
2/3 cup (150 grams) unsalted butter, room temperature
1 1/3 cups (160 grams) confectioners (powdered or icing) sugar, sifted
1 1/2 teaspoons pure vanilla extract
Read more: http://www.joyofbaking.com/ChocolateCupcakes.html#ixzz0eocQGWX5
Chocolate Frosting: Melt the chocolate in a heatproof bowl placed over a saucepan of simmering water. Remove from heat and let cool to room temperature.
In the bowl of your electric mixer, or with a hand mixer, beat the butter until smooth and creamy (about 1 minute). Add the sugar and beat until it is light and fluffy (about 2 minutes). Beat in the vanilla extract. Add the chocolate and beat on low speed until incorporated. Increase the speed to medium-high and beat until frosting is smooth and glossy (about 2 -3 minutes).