1 (12 oz.) pkg. semi sweet chocolate chips
1 (14 oz.) can sweetened condensed milk
1 1/4 c. chopped walnuts (optional)
1 tsp. vanilla

In large glass measuring cup, combine chocolate chips and sweetened condensed milk. Microwave on high for 3 minutes. Stir until chips melt and mixture is smooth. Stir in vanilla and nuts (if desired). Spread evenly into foil lined 8 inch square pan. Chill until firm (about 2 hours).