1 (12 oz.) pkg. chocolate chips
1 c. sweetened condensed milk
3 tbsp. butter
2 tsp. vanilla extract
3/4 c. walnuts, chopped (if desired)

Melt chocolate chips in top of double boiler over very low heat. Stir until melted. Remove from heat. Stir in condensed milk, butter and vanilla. Blend until butter is mixed with the chocolate. Stir in nuts. Spread mixture immediately into a lightly oiled 8 inch square pan. Cool at room temperature. Cut into even squares.