These miniature tarts, made by lining muffin-tin cups with pastry squares, contain pumpkin-pie spices (cinnamon, clove, ginger, nutmeg) but not pumpkins; instead, a sweet custard forms the filling.
Roll out piecrust to a 1/8-inch thickness on a lightly floured surface. Roughly cut into twelve 5 1/2-inch squares, and fit into alternating cups of 2 standard 12-cup muffin tins, folding dough to fit and letting excess hang over edge. Refrigerate until firm, about 1 hour. Generously brush edges with beaten egg, and sprinkle with sanding sugar.
Preheat oven to 350 degrees. Line pie shells with parchment, leaving an overhang on all sides, and fill with pie weights or dried beans. Bake until edges of shells are golden, about 20 minutes. Remove weights and parchment, and bake until bottom of shells are golden, about 20 minutes more. Let cool completely on a wire rack.
Reduce oven temperature to 325 degrees. Whisk together granulated sugar, spices, and salt. Add egg yolks, and whisk to combine. Heat cream and milk until almost boiling, then gradually whisk into egg-yolk mixture. Pour custard through a fine sieve, then divide among shells.
Bake pies until custard is just set but still slightly wobbly in center, about 25 minutes (filling will continue to set as it cools). Let pies cool completely on wire rack, then remove from tins. Before serving, top with whipped cream and nutmeg.