• Preheat the oven to 350° F.

How to Make the Crust

• Use an electric mixer to mix the flour, sugar, salt, and butter in a medium or large bowl until the butter is the size of peas and the dough sticks together when pressed.
• Dump the dough into a parchment-lined, 9x9 square pan, and press it into the bottom.
• Bake the crust for 20 minutes or until it turns golden brown around the edges. Don’t turn off the oven yet.

How to Make the Lime Filling

• While the crust is baking, whisk the sugar and lime juice together in a medium saucepan over medium heat until it starts to simmer. Lower the heat to low and let it continue simmering.
• In a medium bowl, beat the eggs. Scoop out 1⁄3 cup of the lime and sugar mixture, and slowly pour it intothe beaten eggs while whisking quickly. This will heat (temper) the eggs so they won’t cook when addedto the saucepan.
• Slowly pour the tempered egg mixture into the saucepan with the remaining lime juice and sugar mixture, whisking constantly. Continue whisking until the mixture is thick, about 7 minutes and coats the back of a spoon without immediately running off of it.
• Remove the mixture from heat, and whisk in the butter. Once the butter is completely mixed in, add the lime zest and salt. Add 1 small drop of blue food coloring, if desired, to make the bars green. Whisk until everything is combined. Pour the filling over the crust, and bake the bars for 10 minutes or until thefilling starts to bubble around the edges.
• Let the bars rest at room temperature for an hour, then cover them with plastic wrap and refrigerate for at least 2 hours or until the bars are completely set.
• Dust the bars with powdered sugar, slice, and serve chilled or at room temperature.