Put the graham crackers, sugar and butter into a heavy nonstick skillet over medium heat. Stir and toast till lightly browned.
Line 24 miniature muffin cups with fluted foil liners or use 24 (2-ounce) unlined ceramic cups. Divide the crumb mixture between the cups and tamp down firmly using a spoon or something similar with a flat end.
Preheat your oven to 350F (180C).
Make the lime filling. In a glass 2-cup measure, mix the egg yolks, condensed milk, lime juice and lime zest until well blended.
Pour mixture into the crumb u2013lined cups, filling them to the very top. Bake for 15 to 20 minutes or until set. Cool thoroughly and then chill.
Just before serving, whip the cream with the sugar and vanilla. Spoon whipped cream over each little pie. Garnish with lime zest. This recipe makes 24 (2-ounce) servings.