Preheat the oven to 350 degrees and spay your 9x11 baking dish with pam spray
In a large bowl, combine the 2 C of flour, 1/2 C powder sugar and salt
Using a pastry cutter or fork, cut in the butter until the crust mixture looks like crumbs
Pour the crust into the pan and pat evenly into the dish
Bake the crust for 10 minutes
While the crust is baking make the filling
In another large bowl, whisk together the eggs, lime juice, 1/4 C flour, 2 C sugar, 2 tsp key lime zest, baking powder
Whisk until fully incorporated
Pour mixture onto the crust and return to oven and bake for 25 minutes or until set
Once the bars are cooled sprinkle with powder sugar and cut into squares
Top with key lime slices and enjoy!