1. Preheat the oven to 350°F (180°C). To make the crust, mix the graham cracker crumbs, sugar, and butter in a bowl until combined. Press firmly and evenly into the bottom and sides of a 9in (23cm) tart pan with a removable bottom. Place on a baking sheet and bake until the crust looks set, about 12 minutes.

2. Meanwhile, grate the zest of 6 key limes (or 2 limes) in a bowl. Juice 14 key limes (or 5 limes). You should have ½ cup lime juice.

3. Add the condensed milk, yolks, and lime juice to the bowl and whisk well. Pour the filling into the crust. Return to the oven and continue baking 15–20 minutes, or until the filling is set.

4. Transfer to a wire rack and let cool completely. Whip the cream, confectioner's sugar, and vanilla until soft peaks form Spread over the cooled pie. Thinly slice the reserved lime and use to garnish the pie. Remove the sides of the pan, slice, and serve.