1. Heat oven to 350°F. Grease bottom of 8-inch square baking pan.
2. Melt butter and chocolate in a medium saucepan over low heat, stirring occasionally. Stir in sugar, and then add eggs, one at a time, beating after each addition. Stir in vanilla, then combine flour, baking powder and salt, and add to chocolate mixture, stirring until well blended. Spread batter in prepared pan.
3. Bake for 20 minutes or until brownie begins to pull away from sides of pan. Remove from oven and sprinkle with crushed toffee bar bits. Cover tightly with foil and cool completely in the pan on a wire rack. Remove foil and cut into squares.