Batches of these sweet tartlets are made with a variety of heirloom squashes chosen for their hues; ours include White Acorn, Golden Nugget, and Red Kabocha.
Preheat oven to 375 degrees. Fit a medium pot with a steamer insert, and fill with water to just below the insert. Bring to a boil. Add squashes to insert; steam until soft, 15 to 20 minutes. Let cool completely.
On a lightly floured surface, roll out 1 disk of dough to a large rectangle, about 1/8-inch thick. Transfer to a baking sheet, and refrigerate until firm, about 30 minutes. Repeat with remaining disk.
Cut dough into twelve 5-inch rounds. Fit a round into each 4 1/2-inch tart shell, pressing into corners; trim flush with top edge. Refrigerate until firm, about 30 minutes. Line each shell with parchment paper, and fill with pie weights or dried beans. Freeze 10 minutes.
Bake tart shells 10 minutes. Remove weights and parchment. Return to oven; bake 5 to 10 minutes more. Transfer to wire racks; let cool completely.
Scoop out flesh of squashes into a food processor, and process until pureed (you should have 1 1/2 cups puree). Transfer to a large bowl. Add all other ingredients, and whisk until combined.
Reduce oven temperature to 350 degrees. Set tart shells on a rimmed baking sheet. Divide filling among shells. Bake until all but centers are set, 15 to 18 minutes. Transfer to wire racks; cool completely.