Step 1

Preheat oven to 350 degrees Fahrenheit. Lightly grease or line an 11x7-inch or 8 to 9-inch square glass baking dish with parchment paper that overhangs 2-inches on both sides.

Step 2

To make the crust: Combine the flour, powdered sugar, salt and butter in a food processor. Pulse until mixture resembles fine crumbs. Press into prepared pan and bake for 18 to 20 minutes, or until golden brown.

Step 3

Meanwhile make the filling: Whisk together the sugar and flour in a bowl. Add the eggs, one at a time, whisking well after each addition. Add the zest, lime juice, and a drop of green (+ yellow) food coloring, if desired. Mix until everything is smooth and combined.

Step 4

Pour filling over hot crust and return to oven to bake for an additional 18 to 20 minutes or until set. When done, the filling will no longer jiggle.

Step 5

Let cool completely in the pan, about 1 hour. Then refrigerate for 1-2 hours and serve cold. Lift bars out of pan with parchment paper for easy cutting and serving. Store leftovers in the refrigerator.