1 (12 ounce) package semisweet chocolate chips
1 (14 ounce) can sweetened condensed milk, divided
2 teaspoons vanilla extract, divided
1 cup chopped walnuts, divided
1 (11.5 ounce) package milk chocolate chips

Line a 9-in. square pan with foil and butter the foil; set aside. In a heavy saucepan, melt semisweet chocolate chips with 1/2 cup plus 3 tablespoons milk over low heat. Remove from the heat; stir in 1 teaspoon vanilla 1/2 cup walnuts. Spread into prepared pan. In a saucepan, melt milk chocolate chips with remaining milk. Remove from the heat; stir in remaining vanilla and walnuts. Spread over first layer. Cover and refrigerate until firm. Remove from pan and cut into 1-in. squares. Store at room temperature.