1 cup semisweet chocolate chips
4 tablespoons butter (no substitutes), divided
1 (14 ounce) can sweetened condensed milk
1 cup all-purpose flour
1 teaspoon vanilla extract
confectioners' sugar
1 cup butterscotch chips
1/2 cup chopped walnuts

Greased 15-in. x 10-in. x 1-in. baking pan; line with waxed paper and spray the paper with nonstick cooking spray. Set aside. In a microwave or heavy saucepan, melt the chocolate chips and 2 tablespoons of butter; stir until smooth. Stir in milk, flour and vanilla; mix well. Spread into prepared pan. Bake at 325 degrees F for 8 minutes or until a toothpick inserted near the center comes out clean. Cool in pan on a wire rack for 5 minutes. Turn onto a kitchen towel dusted with confectioners' sugar. Gently peel off waxed paper. Roll up brownie in the towel, jelly-roll style, starting with a long side. Cool completely on a wire rack. Melt butterscotch chips and remaining butter. Unroll brownie; spread filling to within 1/2 in. of edges. Sprinkle with walnuts. Reroll; wrap in foil. Refrigerate for 2 hours or until firm. Unwrap and dust with confectioners' sugar. With a sharp thin knife, cut into 1/4-in. slice.