Preheat oven to 350 degrees.
In a food processor, crush the graham crackers until you have fine crumbs (alternatively, put them in a plastic ziplock bag, press the air out, seal, and smash with a rolling pin).
Mix with melted butter until it has the texture of wet sand.
Press the graham cracker mixture into a 10-inch tart ring (a 9-inch may also work, but you may have filling left over, which you can bake in ramekins to make a simple, yummy lime custard!).
Bake the crust for 7 minutes, remove from the oven, and set aside.
Meanwhile, combine the condensed milk, sour cream, lime juice, and lime zest.
Pour into the baked tart shell and return to the oven for 5-8 minutes, until set (not browned!).
Let the pie cool completely.
Whip the cream until soft peaks form.
Top the pie with the whipped cream.
Serve!
