Begin by making the crust. Preheat your oven to 325. Line a 9 x 9” baking pan with two sheets of parchment paper so that each piece fits in the bottom of the pan and comes up two sides.

Combine the chocolate cookies, melted butter, and brown sugar in a bowl and mix well. Press into the bottom of the prepared pan and bake for 7-10 minutes. Remove and set aside while you prepare the filling.

Put the egg yolks in a bowl and whisk. Add the condensed milk and lime juice and zest and stir.

Pour the filling into the crust and return it to the oven and bake another 12-15 minutes until set but still jiggly. Let cool completely, then refrigerate for 2-4 hours, or overnight, before cutting into squares. Dust with powdered sugar if desired.