I also made my first attempt at lemon bars this weekend, and they came out fantastic, so I thought I'd share the recipe. These come out significantly more tart then lemon bars usually are, so you could reduce the amount of lemon juice if you like.
Tart Lemon TartI was actually really surprised how easy it is to make these and how delicious they come out. I'm sure they would also be delicious with key lime juice rather than lemon. You could also make this in a round cake pan and cut it into slices, to make it more like a tart.
1/2 stick (1/4 c) salted butter, softened
1/4 c powdered sugar
1 1/4 c flour
1 3/4 c sugar
1/2 c lemon juice
1/4 teaspoon lemon extract
Preheat oven to 325°. Line an 8x8 Pyrex cake pan with nonstick aluminum foil. In a bowl, combine butter, powdered sugar and 1 cup of flour with your fingers until crumbly, then press it into the pan as evenly as possible. Bake for 15-20 minutes, until dry but not browned. Meanwhile, using the same bowl if you like, beat the eggs until foamy, then mix in the sugar, remaining flour and lemon juice and extract. Pour this mixture over the crust and bake for another 20 minutes or so, until the lemon custard is set in the center. While the bars are still warm, sprinkle powdered sugar over the top. Let cool for at least an hour before cutting.