For the perfect finishing touch, dust these rich bar cookies with powdered sugar.
In a medium saucepan melt butter or margarine and brown sugar; cool to lukewarm. Stir in eggs and vanilla. Sprinkle flour, baking powder, and salt over butter mixture. Stir just until mixture is smooth. Stir in all but 2 tablespoons of the chocolate pieces; transfer to a greased 11x7x1-1/2-inch baking pan. Sprinkle with reserved chocolate pieces.
Bake in a 350 degree F oven for 25 to 30 minutes or until a toothpick inserted near center comes out clean. Cool in pan on a wire rack. If desired, sprinkle with powdered sugar. Cut into bars. (To tote, cover pan with plastic wrap.) Makes 18 bars.
Store in airtight container up to 3 days at room temperature or 1 week in refrigerator.