Cut the cold butter into the flour, sugar, and salt until the mixture looks like coarse crumbs.
Add ice water one tablespoon at a time until the dough just holds together. Shape into a disc, wrap, and chill at least 30 minutes.
Make the Filling
Whisk the pumpkin puree, brown sugar, egg, heavy cream, vanilla, pumpkin pie spice, and salt in a bowl until smooth and pourable.
Assemble and Bake
Roll the chilled dough into a rough 12-inch circle on parchment paper.
Spread the filling in the center, leaving a 2-inch border. Fold and pleat the border up over the edge of the filling.
Brush the crust with beaten egg and sprinkle with coarse sugar. Bake at 375°F for 35 to 45 minutes, until the crust is deep golden and the filling is set. Cool before slicing.
Notes
Pure pumpkin: Use plain pumpkin puree, not pre-spiced pie filling.
Keep it cold: Chill the dough if it softens while you work so the crust bakes up flaky.
Thin filling: Spread the filling in a shallow layer so it sets before the crust over-browns.
Storage: Keeps 3 to 4 days refrigerated; reheat at 325°F to re-crisp.