Cut the squash in quarters and remove the seeds. Brush the insides with a little oil and arrange them on a baking sheet, skin side up. Roast in the preheated oven until the squash is soft all the way through, about 1 hour. Remove from the oven and let cool. (This can be done 1 or 2 days ahead.) When the squash is cold, remove it from the skin and puree in a food processor. You'll need 2 1/2 cups of squash puree for this recipe. If the mixture is dry while pureeing, add a ladleful of the pudding mixture.
Pudding: Preheat the oven to 350 degrees F.
In a large bowl, combine the heavy cream, eggs, brown sugar, spices, and vanilla and mix well. Stir in the pumpkin puree. Combine the bread, raisins and ginger in the baking dish. Pour the pudding mixture over the bread to cover and let it sit for 15 minutes.
Cook's Note: You may not use all of the filling. Add more filling if there's room in the dish, once the bread has soaked.
Bake in the preheated oven until the custard is set, about 20 to 25 minutes.
It's fall in a dessert! To serve, spoon the pudding into bowls and sprinkle a dusting of confectioners' sugar on top.