Caroline's Chocolate Fudge Frosting

Melt chocolate and butter in the microwave, or in the top of a double boiler. In a large bowl, combine confectioners' sugar, vanilla and 1/2 cup of the milk. Blend in the melted chocolate mixture. Add remaining milk, a little at a time, until desired consistency is achieved.
Let stand until spreadable (frosting will thicken as it cools).