To prepare the crust

1. Preheat the oven to 350 degrees. Lightly spray 4 (4-1/2 inch) tart pans with removable bottoms with baking spray.
2. Pulse graham crackers in a food processor to crumbs. Add the remaining ingredients and pulse to combine. Divide the crust mixture among the 4 pans and press into the bottoms of the pans with your fingers. Bake in the oven for 8-10 minutes, or until the crust is set. Set aside to cool slightly.

To prepare the key lime pie

1. In a medium sized glass bowl, whip the egg yolk for about 1 minute with a wire whisk. Add the sweetened condensed milk, key lime juice, and zest. Whisk to combine.
2. Divide the mixture between the 4 tart pans. Bake in the preheated oven for 12-14 minutes, or until the outer edges of the tart have set. Allow to cool at room temperature for 30 minutes and then chill in the refrigerator until cold, or at least an hour.
3. When ready to eat, unmold tarts by turning upside down on a piece of wax paper and pressing gently on the removable bottom with your fingers. Once removed, flip out on to a plate. Sprinkle 1 tablespoon of sugar on each tart and caramelize using a kitchen torch. Allow to rest for 3-4 minutes and then serve.