Preheat oven to 325°F. Put a kettle of water on to heat for the water bath. Line a roasting pan with a folded kitchen towel.
Heat milk over low heat in a small saucepan until barely steaming but not boiling.
Whisk eggs and syrup in a large bowl until smooth. Gently whisk in the warm milk (a little bit at a time so the eggs don't cook). Add pumpkin puree, cinnamon, nutmeg and salt; whisk until blended.
Divide the mixture among six 6-ounce (3/4-cup) custard cups. Skim foam from the surface. Place custard cups in the prepared roasting pan. Pour enough boiling water into the pan to come halfway up the sides of the custard cups. Place the pan in the oven and bake, uncovered, until custards are just set but still quiver in the center when shaken, 45 to 50 minutes. Transfer custards to a wire rack and let cool for 45 minutes. Cover and refrigerate for at least 1 hour, or until chilled.
To serve, top each custard with a dollop of whipped cream and a sprinkling of crystallized ginger.
Ingredient note: If you can find it, use Grade B dark amber syrup to get the best maple flavor.