In a food processor, pulse the graham crackers until finely ground. Add the butter, sugar, lime zest, and salt and process until combined well.
Press the graham cracker mixture into the bottom and up the sids of a 9-inch tart pan or 6 tiny tartlets as I did. When you press the mixture use a flat bottom measuring cup to help press it in, for the mini tartlets I used the back of a spoon.
Bake for 10 minutes and take out of the oven to set.
To make the filling beat the egg yolks until fluffy and gradually add the condensed milk and beat until thick. Next add the lime juice and continue beating until combined.
Pour the filling mixture into the baked crust and return to the oven to bake for another 10 minutes, or until it is set.
Transfer to a wire rack to cool slightly and increase the oven temperature to 450 degrees for the meringue.
To make the meringue beat the egg whites and salt until foamy. Add the cream of tartar and beat until soft peaks form. Add the sugar 1 tablespoon at a time beating until stiff with glossy peaks. Add the vanilla at the end.
Now scoop the meringue onto the lime filling, making fancy swirls and peaks. I used a spoon to do this part. Bake for 3 to 5 minutes until the peaks are browned in spots.
Cool at room temperature. You can serve it at room temperature or chilled.
Recipe from Beekman 1802 Heirloom Dessert Cookbook