Preheat the oven to 375 degrees F.
Combine the graham cracker crumbs, sugar, and butter in a medium bowl. Press together with your hands. Press the mixture firmly onto the bottom and up the sides of a 9-inch pie pan, and bake until brown, about 15 minutes. Remove the crust from the oven and allow to cool completely before filling.
Reduce the heat to 325 degrees F.
Combine the condensed milk, lime juice, and eggs in a large bowl. Whisk until well blended, then pour the filling into the cooled pie shell. Bake for 15 minutes; allow to cool in the refrigerator for at least 2 hours.
Once chilled, combine the sour cream and confectioners' sugar and spread over the top of the pie with a spatula. Sprinkle the lime zest on top as a garnish and serve chilled.
Makes one 9-inch pie, 8 servings