Preheat oven to 425 degrees Fahrenheit. Place pumpkin quarters on two baking sheets. Drizzle with oil and season with salt and pepper. Place pumpkins cut side down, on sheets. Roast, turning occasionally, about 45 minutes.
Let pumpkin cool. Scoop out flesh. Taste each pumpkin to make sure they are not bitter or tasteless. (It’s a good idea to always roast a bit more pumpkin, as there is always the chance of the occasional not-so-good pumpkin.)
Bake apples in a separate baking dish alongside pumpkin, until soft, about 30 minutes.
Heat oil in a large pot, over medium heat. Add carrots, celery and shallots, and season well with salt and pepper. Cook, covered, for seven minutes. Add garlic, sage, nutmeg, and cardamom, and cook for one more minute. Add pumpkin, apple, vinegar, and water. Bring to a boil and simmer for 15 minutes.
Using an immersion blender, blend until smooth. Stir in the apple cider. If too thick, stir in water, one tablespoon at a time. Cook for an additional minute or until warm. If you’d like it thicker, simmer for a few minutes, uncovered, to reduce. Stir-in or marble-in heavy cream.