1. Preheat oven to 350°F.
2. In a medium bowl, mix together flour and powdered sugar for crust.
3. Cut in butter (I use my hands; you could also use a fork or a food processor) until the mixture forms a dough.
4. Crumble dough evenly into an ungreased 9x13 pan, then press with your hands to cover the surface.
5. Bake crust for about 10 minutes, until puffed and golden around the edges.

Prepare the Filling:

1. In the bowl of a stand mixer, beat eggs, sugar, key lime juice, and zest on medium speed for about a minute and a half.
2. Pour over crust and bake for about 20 minutes or until filling is set and no longer runny on top. Remove from oven, let cool, and chill bars until cold and firm.

Make the Meringue:

1. In a metal mixing bowl set over a pot of simmering water, whisk together egg whites and sugar for meringue.
2. Whisk until sugar seems to have melted and the mixture forms a syrup, about 10 minutes.
3. Remove from stove and set bowl on your mixer. Beat on high with the whisk attachment until it forms stiff peaks.

To Serve:

1. Cut chilled bars into squares.
2. Pipe or spoon meringue on bars and brown with a small kitchen torch (alternately, you could pop the bars under your oven broiler, just keep a close eye so the meringue doesn’t burn).
3. Serve.