adapted from williams-sonoma.com
4 oz. unsweetened (or bittersweet) chocolate, chopped
3 cups confectioners’ sugar
1 stick butter or margarine
2-3 Tbs. [soy] milk, plus more, if needed
1 tsp. vanilla extract
1 tsp. salt
Heat chocolate a double boller until melted. Let cool to room temperature. In a bowl, of an electric mixer fitted with the flat beater, combine the confectioners’ sugar, butter, the milk, and vanilla and beat on low speed until combined, about 1 minute. Stop the mixer and scrape down the sides of the bowl. Increase the speed to medium and beat for 2 minutes, then reduce the speed to low. Add the chocolate and beat until combined, then increase the speed to medium and beat for 1 minute more.
If the frosting is dry, add more milk, 1 tsp. at a time, until it is creamy but still holds peaks.