Heat oven: To 350°F (176°C).

Make the crust: Combine cracker crumbs, sugar and salt in a medium bowl and stir until combined. Stir in the butter until it's evenly coated. Pour crumbs into a 9 inch pie dish and press them down into the bottom and up the sides. You can use the edge of a flat-bottomed measuring cup or drinking glass to make the corners neat or just use your fingers. Bake crust for about 10 minutes, until it's just lightly browned. Set aside on cooling rack while you make the filling. Leave oven on.

Make the filling: Zest limes using a fine grater or microplane. Once you have 1 1/2 tablespoons zest, put it in the bottom of a medium bowl (or the bowl for the stand mixer). Add the yolks and using a handheld mixer or stand mixer with the paddle attachment, beat the yolks and zest until they turn pale and thick, about 4-5 minutes. Add the sweetened condensed milk and beat again until thickened, about 3 minutes more. Add the lime juice and whisk into the mixture until combined. Pour into the cooled graham crust and bake pie for about 10 minutes, until just set but not browned at all. Let pie cool for about an hour on the countertop and then refrigerate for at least 30 minutes before topping with the cream. (You can speed this process by putting the pie in the freezer for about 10 minutes or so). It should be fully cool at this stage.

Make the whipped cream: Add the cream to a bowl and, using a handheld mixer or stand mixer with the whisk attachment, beat until barely thickened. Add the sugar and vanilla and continue to beat until soft peaks form. Spread around the outer rim of the pie with a dollop in the middle or just mound over the top of the pie. Chill for another 2 to 3 hours so the cream can set (if you want neat slices. If not, dig in now).

Keeps in fridge for a week.