1. Heat oven to 350 degrees F. Line a 9-inch square baking pan with foil, leaving one inch of foil over sides of pan. Grease bottom and sides of foil with vegetable shortening. Whisk together flour, baking powder, and salt in medium bowl; set aside.
2. Melt butter in medium saucepan over medium heat. Stir in sugar and cook until well combined, 2 to 3 minutes. Stir in peanut butter and cook until mixture is smooth, 3 minutes. Remove pan from heat. Beat in eggs and vanilla with a spoon. Stir in flour mixture, until smooth. Pour batter into prepared pan. Sprinkle top with chips. Bake until edges are golden and toothpick inserted in center comes out clean, 25 to 30 minutes. Cool completely on wire rack. Remove from pan; peel off foil and cut into twelve 2x2-3/4-inch bars. Makes 12 bars.