Chocolate Sour Cream Frosting

1 c. semisweet chocolate chips
1/4 c. margarine
1/2 c. sour cream
2 1/2 c. powdered sugar

In a bowl cook chocolate chips and margarine until melted, stirring every 30 seconds. Cool 5 minutes. Stir in sour cream. Gradually add powdered sugar, beating till smooth.