Preheat oven to 300º F.

Whisk sugar, egg yolks, vanilla, spices, and salt together in a large mixing bowl or the bowl of your stand mixer. Set aside.

In a medium-size saucepan, whisk together the milk and heavy cream, pumpkin purée, and maple syrup. Cook over medium-low heat, stirring occasionally until the mixture is hot but not boiling, about 7 minutes.

Ladle into sugar and yolk mixture, stirring constantly. (If you pour it all in at once the yolks will cook; you don't want that to happen.) Once egg mixture and hot mixture are roughly the same temperature you can add it a bit more quickly.

Pour 3/4 inch of hot water into a large, shallow casserole dish. Divide the custard evenly among six custard cups and arrange the filled cups, evenly spaced, in the baking dish.

Bake the custards, uncovered, on the center oven rack for about 45 to 50 minutes. The centers may jiggle a bit, but shouldn't be too fluid. 

Transfer the custard cups to a wire rack to cool.

When the custards reach room temperature, cover and refrigerate for at least six hours.

Serve topped with whipped cream (or ice cream!) if you like.