To make soup: Heat butter in a large 6 quart pot or Dutch oven, over medium high heat. Add onions. Cook for 2 minutes just until beginning to soften and brown. Add garlic, cooking for 1 minute longer. To the pot add squash, sweet potato and apple. Stir to coat with butter.
To the pot add chicken stock and a large sprig of fresh thyme. Season with ½ teaspoon salt,. Cover pot and simmer on medium-low heat for 45-60 minutes, until squash is fork tender. Remove thyme stems from pot.
Ladle cooked vegetables and broth into a stand blender and puree. Return puree to pot adding heavy cream, reserved salt, pepper, turmeric, cayenne, ginger and nutmeg. Mix together simmer over medium for 5 minutes.
Keep warm until serving garnished with fresh thyme, roasted seeds and sour cream.
While soup cooks roast seeds: Remove seeds from stringy squash fibers. Rinse well and pat dry with paper towels. Toss with 1 ½ teaspoon olive oil, salt and smoked paprika. (eyeball amounts) Spread in a single layer on a baking sheet. Roast for 10-15 minutes in a preheated 375°F oven. Set aside to cool, then serve as a garnish for soup.