Light and intensely flavorful, these individual custards are an autumn treat. The butternut squash is roasted in the oven to concentrate its sweetness without adding moisture.
Note that the custards need to be refrigerated until they're completely cold before unmolding and serving, so plan accordingly. These triple-crème caramels can be made up to 3 days in advance of serving.
Position a rack in the middle of the oven and preheat to 400 degrees F. Line a rimmed baking sheet with parchment paper or a Silpat.
Place the butternut halves on the baking tray, cut side down, and roast until the squash is tender when pierced with the tip of a knife, 45 to 55 minutes.
Let the butternut cool, then remove the flesh with a spoon, and discard the skin. Purée the squash in a food processor and reserve 3/4 cup; refrigerate the remainder for another use.
Place the milk and the 1/4 cup sugar in a small saucepan and warm over medium heat, stirring until the sugar dissolves. Remove the pan from the heat.
Place the 3/4 cup of purée in a food processor and add the eggs, egg yolk, and egg whites. Process until smooth. Add the maple syrup, vanilla, ginger, cinnamon, allspice, and the warm milk mixture, and process until combined. Transfer the custard to a clean container and refrigerate while you make the caramel topping.
To make the caramel, combine the 1 cup sugar, water, and corn syrup in a heavy-bottom saucepan and bring the mixture to a simmer over medium heat, stirring until the sugar dissolves. If you see any sugar crystals on the side of the pan, wash them down with a wet pastry brush. Reduce the heat to low and simmer until the syrup turns a medium amber color, about 30 minutes. Do not stir!
While the syrup is cooking, set eight 1/2-cup ramekins in a roasting pan. As soon as the caramel is ready, pour it into the ramekins, adding just enough syrup to coat the bottoms of the dishes. If the caramel hardens, reheat it gently.
Position a rack in the middle of the oven and preheat to 325 degrees F.
Divide the custard among the ramekins. Pour enough hot water into the roasting pan to come halfway up the sides of the dishes. Cover the pan tightly with a sheet of aluminum foil. Bake the custards for 30 minutes, or until they're set but slightly jiggly in the center. Remove the ramekins from the pan and let them cool to room temperature on a wire rack. Refrigerate the custards until thoroughly cold; cover with plastic wrap if you're storing them overnight or longer.
To serve, pour one inch of boiling water into a pan or bowl. Dip the bottom of one ramekin in the water for 10 to 15 seconds. Run a thin knife around the edge of the ramekin. Invert the dish onto a plate and let it rest for one minute before you remove the ramekin. Repeat with the remaining crème caramels, then serve.