1. Make the maple caramel by putting the sugar, maple syrup and water in a small, heavy-duty saucepan fitted with a candy thermometer. Cook over medium heat without stirring, although you can swirl the pan to combine the ingredients at the beginning. It’s ready when the temperature reaches 230ºF (110ºC).
2. Immediately remove from heat, sprinkle in the flaky sea or kosher salt and pour the caramel into an 8-inch (20cm) cake pan (not a springform pan) that has sides at least 2-inches (5cm) high. (See note at end of recipe for other options.) Let cool for until room temperature, about 30 minutes.
3. Preheat the oven to 350ºF (180ºC).
4. Using a stand mixer with the whip attachment, or by hand in a medium-sized bowl using a sturdy whisk, mix together the sweetened condensed milk, evaporated milk, canned pumpkin and mascarpone until smooth. Whisk in the eggs, vanilla extract, cinnamon, allspice, and orange zest.
5. Place the caramelized cake pan in a roasting pan and pour the custard over the back of the large spoon or spatula into the cake pan, over the caramel. (Pouring it over the spoon or spatula will disperse the liquid so it doesn’t disturb the caramel, as it would if it was poured in a steady stream.)
6. Add very hot tap water to the roasting pan so that it reaches halfway up the outside of the cake pan and bake the custard on the middle rack of the oven until just barely set, about 70 to 75 minutes. When done, it’ll be slightly jiggly in the center, but set around the edges.
7. Remove the flan from the water bath and let cool completely on a wire rack, then chill 3-4 hours (or overnight), before serving.
8. To serve, run a sharp knife around the outside of the flan to release it from the sides of the cake pan. Lay a serving platter upside down on top of the flan and using both hands, flip the flan and the serving platter over simultaneously. Holding both the cake pan and platter, shake to release the flan. If it doesn’t release easily, slip your finger on one side of the flan, near an edge, to break the airlock; you should feel (and hear) the flan release slowly. Don’t rush it, but let it release and fall out gently, so it stays together.
Storage: The pumpkin flan can be made up to three days in advance and kept refrigerated.