Preheat oven to 350 degrees.

Line up graham crackers crusts on a baking sheet.

In a small bowl, mix (almost) one can sweetened condensed milk with one whole egg. The less sweetened condensed milk you add, the more tart it will be. I like tart, so I didn't use the whole can.

Add lime juice and continue mixing.

Zest one lime and add to the mixture.

Once combined, fill your graham cracker crusts to the top (these will not bake over).

Bake 8-10 minutes or until the insides are slightly wiggly. You don't want to burn the crusts. Mine took exactly 9 minutes to bake.

Transfer to the fridge to cool for a few hours before serving.

Top with whip cream.