Don't hesitate to serve this pumpkin custard any time of year.
Set a large pan of cold water near stove. Combine 1/2 cup of the sugar and the 1/4 cup water in a small, heavy saucepan over low heat. Cook, stirring occasionally, until sugar dissolves. Cover pan and bring to a boil. Leave cover on until condensation washes down insides of pan. Uncover pan, turn heat to medium high, and boil, without stirring, until syrup turns a deep amber. Carefully plunge bottom of pan into the cold water to stop the cooking.
Quickly pour caramel into a 9-inch-round glass baking dish; holding dish with potholders, swirl to coat bottom and halfway up sides of pan. Set aside to cool.
Heat oven to 325 degrees. In a large bowl, combine pumpkin, remaining 3/4 cup sugar, spices, salt, eggs, and egg yolks. Mix in vanilla and scalded milk, then pass mixture through a fine sieve. Pour into caramel-lined dish and set in a roasting pan. Fill roasting pan with very hot water to halfway up sides of dish.
Cover roasting pan loosely with foil and bake for 60 to 70 minutes, or until center of flan is nearly set: a thin-bladed knife should come out clean. Let cool to room temperature in water bath, then chill overnight.
To unmold, run a sharp knife around flan, put a plate over top, quickly flip over, and carefully remove dish.
This flan can be made ahead of time and refrigerated in the pan until ready to serve.