1. Melt chocolate pieces in the top of a double boiler over simmering water; remove from heat.
2. Blend in peanut butter, then beat in 10X sugar and milk until smooth. Spread the mixture in a buttered, 8x8x2-inch pan.
3. Chill for at least 30 minutes, or until firm. Cut into 1-inch squares. Cover; store at room temperature.