Preheat oven to 350 F. Slice the pumpkin in half and scoop out the seeds and stringy pulp. Brush the cut surfaces lightly with oil, salt & pepper. Bake at 350, cut-side-down, until fork-tender, about 45 minutes. Set aside to cool. Meanwhile, boil the potato in a small pot until soft, then drain & mash. Peel the skins from the cooled pumpkin and puree the pulp in a blender or food processor. You’ll want to end up with about 4 cups of puree. If you have extra, it freezes well! Save it for a Thanksgiving pie. Heat the ghee or butter in a large pot over medium-high heat. Add the onion and cook until translucent, stirring occasionally. Add the garlic, salt, pepper, and thyme, then cook an additional minute or two. Add the pumpkin puree and mashed potato, then whisk in the stock. Heat it through, the blend with an immersion blender, or work in batches in a regular blender. Add the milk and simmer another 5 minutes, or so. Just before you are ready to serve, stir in a splash of vinegar, then top with a dollop of crème fraîche and a sprinkle of fresh parsley.