- Preheat your oven to 300F (150C). Line the baking sheet with parchment paper and arrange the start rings on it.
- In a bowl, combine the graham crumbs, sugar, and butter. Stir until the graham crumbs are moist and stick together slightly when clumped.
- Place about 1/2 cup of the crumb mixture into one of the rings. Using your fingers, gently press crumbs up the sides of the ring to cover. Fill the bottom with the crumbs that remain. Repeat for the remaining rings. If you’re using a pie plate, lightly butter the plate and press the crumbs evenly along the bottom and sides using your fingers.
- Bake the tart shells for 12 minutes (14 minutes if using a pie plate). Remove from the oven and increase the oven’s temperature to 325F (160C).
- To make filling, whisk together the egg yolks, lime zest, and condensed milk in a bowl until smooth.
- Using an ice cream scoop or a large spoon, fill the baked tart shells level with the top.
- Bake the tarts for ten minutes (18 minutes if using a pie plate). Allow them to cool for ten minutes before gently removing the tart rings. Refrigerate for at least two hours, until finally chilled. Using a pie server or a large spatula, transfer the chilled tarts to individual plates or small cake boards and serve.
Storage – Key lime tarts will keep in the refrigerator for up to four days.