1. Heat oven to 350°F. Beat butter in large bowl on medium speed until creamy. Beat in brown sugar, vanilla and egg yolk until well mixed.
2. Stir in flour and 1 cup of the toffee bits. Press into ungreased jelly-roll pan, 15-1/2x10-1/2x1 inch.
3. Bake 18 to 20 minutes or until light brown. Immediately sprinkle chocolate chips over top. Let stand until softened, about 5 minutes; spread evenly. Sprinkle remaining toffee bits over top. Cool completely. Cut into 3-inch squares; cut each square into 4 triangles. Makes 60 triangles.