Heat oven to 350 degrees F. Line 13 x 9 x 2-inch baking pan with aluminum foil so foil overhangs short ends. Lightly coat with nonstick vegetable-oil cooking spray.
Combine flour, butter, sugar and salt in food processor. Whirl with on-and-off pulses until the mixture resembles coarse meal. Or in medium-size bowl cut butter into flour mixture with pastry blender or 2 knives held scissor fashion.
Scrape crust into prepared pan; spread level and pat down to compact evenly.
Bake crust in 350 degree F oven for 20 minutes or until lightly colored.
Combine sugar, flour, baking powder, lemon juice, eggs and rind in food processor. Whirl until well blended. Pour mixture over hot crust.
Bake in 350 degree F oven for 20 minutes or just until set in the center. Transfer pan to wire rack to cool completely. Carefully lift foil to remove whole Lemon Bar. Cut into squares. Dust with confectioners sugar and remove from foil. Bars can be refrigerated in airtight container for up to 1 week. Makes 35 bars.