Preheat oven to 350

Crust: Blend butter, flour, salt, and powdered sugar in a food processor until crumbly and resembling wet sand.  Add the cold water and continue to process until dough comes together.  Roll out crust and place it into a tart pan or 9″ pie pan and press gently into place.  Pierce all over bottom of crust with a fork.  Line the crust with parchment and fill with pie weights.  Bake the crust for about 15 minutes until set, removing the pie weights for the final 5 minutes of baking.

Filling:  While the crust bakes begin mixing the egg yolks, sweetened condensed milk, lime juice and zest until well incorporated.  Pour the filling into the warm pie crust and return the tart to the oven.  Bake for an additional 15-18 minutes.  You want the tart to be just set with a hint of a jiggle, but no longer wet.  Allow the tart to cool, and then cover and refrigerate to chill.

Topping: Once the tart has chilled, mix the heavy cream and sugar until medium stiff peaks form.  Top the tart with the whipped cream and additional lime zest (optional).