1. Preheat the oven to 350ºF.
2. Beat the 1/4 cup of confectioners' sugar and butter on medium speed until creamy.
3. Gradually add the 1/2 cup of flour and mix on low speed until the mixture is crumbly. Press the mixture into the bottom of an 8-inch square baking pan.
4. Bake until just golden brown, about 10 to 12 minutes. Cool on a wire rack. Lower the oven temperature to 325ºF.
5. Whisk the eggs on medium speed until foamy. Add the sugar, lemon zest, lemon juice, 3 tablespoons of flour, baking powder and salt and combine.
6. Pour the mixture over the baked crust and bake until set, about 20 to 25 minutes. (Do not touch the filling with your fingers or it will stick to them.) Cool on a wire rack.
7. Cut into 16 squares and dust with confectioners' sugar.Serving Size: 1 square