Highlight the bright flavor of key limes with this miniature version of a classic dessert. For the crust, you'll need: 1 ½ cups graham cracker crumbs, 2 tablespoons melted butter and 2 tablespoons granulated sugar. For the filling, you'll need: ½ cup fresh key lime juice, 2 cups whipped topping - plus more for garnish, 1 additional key lime for zest and 1 drop of green food coloring (optional).