Heat oven to 350°F. Grease 13x9-inch pan with shortening. In large bowl with electric mixer, beat granulated sugar, brown sugar and butter on medium speed until well blended. Beat in vanilla and eggs until light and fluffy. On low speed, beat in flour, baking powder and salt until dough forms. With spoon, stir in 1/2 cup toffee bits. Spread in pan.
Bake 20 to 25 minutes or until golden brown and toothpick inserted in center comes out clean.
Remove pan from oven. Immediately sprinkle with chocolate chips; let stand 1 minute. Spread melted chips over bars. Sprinkle 1/3 cup toffee bits evenly over top. Cool completely, about 45 minutes. Cut into bars.