Preheat the oven to 350°F.
Mix the two milks, the eggs, pumpkin puree, vanilla extract, nutmeg, cinnamon and salt in a blender until smooth. Set aside.
Cook the sugar and water in a saucepan over medium-low heat, stirring until the sugar is dissolved. Increase heat to medium-high and boil without stirring until it becomes a light amber color.
Pour the caramel quickly into a flan mold or individual cups, rotating so that the bottom and sides are coated.
Pour the custard mixture into the mold and set it into a roasting pan. Pour boiling water into the roasting pan until it comes halfway up the sides of the flan mold.
Cook for about 50 minutes or until firm.
Remove from the oven, allow to cool, and place flan mold in the refrigerator for at least 8 hours or overnight. Before inverting onto a serving plate, run a sharp knife around the rim of the mold.