Preheat oven to 350 degrees F. Generously butter 13x9inch baking pan. Combine 2 cups flour, butter, 1/2 cup powdered sugar, ground almonds, lime peel and salt in processor and process until moist clumps form. Press onto bottom of prepared pan. Bake until edges are golden, about 20 minutes. Whisk sugar, eggs, lime juice, baking powder and remaining 1/4 cup flour in large bowl until well blended. Pour over hot crust. Bake until topping is set and lightly golden, about 25 minutes. Cool in pan on rack. Sift additional powdered sugar over top. Cut into squares.
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