1. Heat oven to 350°F (180°C).
2. In large bowl, beat butter and brown sugar until fluffy. Beat in egg yolk and vanilla until creamy.
3. Stir in flour and 1 cup (250 mL) of the toffee bits. Press into ungreased 15-1/2 x 10-1/2 inch (39 x 27 cm) jelly roll pan.
4. Bake 18 to 20 minutes or until light brown. Immediately sprinkle semi-sweet chocolate chips over top. Let stand until softened, about 5 minutes; spread evenly over top. Sprinkle with remaining toffee bits. Let cool completely. Cut into 3-inch (7.5 cm) squares; cut each square diagonally into 4 triangles.
Makes 60 triangles.