Preheat the oven to 350 degrees and lightly butter an 8 x 8-inch baking pan.
In a medium mixing bowl, combine the flour, butter, confectioners sugar, and salt and rub the mixture between your fingertips until it is the consistency of large moist breadcrumbs. Press the sweet dough evenly onto the base and about 1 inch up the sides of the prepared baking pan, and place the pan in the freezer for 10 minutes to firm the pastry. Bake in the center of the oven for 30 to 35 minutes, or until the pastry is firm and golden brown all over.
Meanwhile, in a large bowl, beat the eggs together with the sugar until the sugar is dissolved and the mixture is pale. Beat in the baking powder, lime zest, lime juice, and salt. Stir in the pistachio nuts. Pour this mixture over the prebaked crust, making sure that the pistachios are evenly distributed, and return to the oven for 20 to 25 minutes more, or until the filling is set and puffy. Transfer the pan to a rack to cool and refrigerate for at least 1 and preferably 2 hours, or overnight, tightly covered. Just before serving, sift a little confectioners sugar over the top and cut into squares.
c.1997, M.S. Milliken & S. Feniger, all rights reserved