Preheat the oven to 350°F, and grease a half sheet pan (13 x 18 inches), with edges, with floured baking spray.
Melt the butter in a large bowl in the microwave.
Add the confectioners’ sugar and flour to the melted butter and mix until well blended.
Press into the greased half sheet pan.
Bake the cookie base for 15 to 20 minutes or until golden brown.
While the crust is baking, make the lemon filling; stir together the sugar, flour, and
baking powder in a large bowl.
Add the eggs, lemon juice, and lemon zest and mix until well blended.
Pour the mixture over the hot crust and bake for another 20 to 25 minutes.
Let the bars cool completely.
Sprinkle with confectioners’ sugar and cut into 1-inch squares.