Preheat oven to 350°F. Line a 13x9x2-inch baking pan with foil, extending the foil over edges of pan; set aside.
For Crust: In a food processor combine the 1-3/4 cups flour, the pecans, and the 3/4 cup granulated sugar. Add butter slices. Cover; process with several on/off turns until the mixture resembles coarse crumbs. Press crumb mixture into the bottom of the prepared pan. Bake for 20 to 22 minutes or until crust is light brown. Let cool for about 5 minutes while preparing filling.
For Filling: in a medium bowl whisk together eggs, the 1-1/2 cups granulated sugar, the 2 tablespoons lime peel, the lime juice, the 1/4 cup flour, the milk (or rum), snipped fresh mint, baking powder, and salt until combined. Pour filling over hot crust.
Bake for 20 to 25 minutes more or just until filling is set and edges begin to brown. Cool in pan on a wire rack.
Using the edges of the foil, lift uncut bars out of pan; cut into bars. Sift powdered sugar over bars. To serve, sprinkle with powdered sugar. If desired, garnish with additional lime peel and fresh mint leaves.
To Store: Layer bars between sheets of waxed paper in an airtight container; cover. Store in the refrigerator for up to 1 week.
Crust1 3/4 cup all-purpose flour1 cup chopped pecans3/4 cup granulated sugar1 cup butter, cut in slicesFilling4 eggs, lightly beaten1 1/2 cup granulated sugar2 tbsp finely shredded lime peel1/2 cup lime juice1/4 cup all-purpose flour2 tbsp milk (or 4 tbsp coconut rum)1 tbsp fresh mint1/2 tsp baking powder1/4 tsp saltToppingspowdered sugarfinely shredded lime peel (optional)fresh mint leaves (optional)