Heat oven to 350° F. Line 13x9x2-inch baking pan with foil, extending foil beyond sides of pan.
Beat butter, sugar and maple flavor in large bowl until fluffy. Gradually beat in flour, beating until well blended and large crumbs start to form. Stir in toffee bits; pat dough into prepared pan.
Bake 20 to 25 minutes or until light golden brown. Cool 10 minutes; cut into bars or triangles. Cool completely in pan on wire rack.
Lift bars from pan; place on cutting board and peel back sides of foil. Stir together powdered sugar and milk; drizzle over bars. When drizzle is almost set, recut bars and separately slightly. Allow drizzle to set up completely. Makes about 48 bars.