Pulse flour, sugar, and salt in a food processor to combine.
Add the butter and pulse until the butter is in very small pieces (smaller than a pea) and the flour mixture feels sandy, about 20 pulses.
Add the beaten egg and 1 tablespoon ice water. Pulse until the dough begins to come together (if needed add an additional 1-2 tablespoons ice water). Do not allow the dough to form a ball in the food processor!
Once the dough begins to come together, remove from the processor onto a large piece of parchment and knead a few times until the dough forms a ball.
Shape into a disk, about 1-inch thick. Cover and refrigerate for at least 1 hour.
Roll the dough into a 15-inch circle, about ⅛-inch thick, and cut out rounds about ½-inch wider than the top diameter of your tart pans.
Gently press the dough into tart pans and trim away any excess.
Reroll scraps of dough and repeat with remaining tart pans.
Dock dough into tart pans and freeze until firm, about 30 minutes.
Preheat oven to 325 degrees F.
Place a piece of parchment over each tart shell and fill with pie weights.
Bake until edges are lightly browned, about 20 minutes.
Carefully remove parchment and weights and bake until the edges and bottoms of the tart shells are golden, about 20 minutes.
Allow to cool completely before filling with tart mixture.