Preheat the oven to 425°F. Peel and cube squash into 1-inch pieces. Cut onion into four chunks. Place the squash and onion on a large sheet pan. Slice 1/4 inch from the top of the garlic bulb. Drizzle 1 teaspoon olive oil over the bulb, wrap it tightly in foil, and place it on the sheet pan with the squash and onion.
Drizzle the remaining oil over the squash and onions. Season with salt and pepper. Toss to coat. Roast for 15 minutes, toss, then roast for another 15 minutes, until tender. Set the garlic aside.
In a large pot, melt the butter over medium heat. Stir in the nutmeg, cloves, and curry powder for 1 minute, until fragrant. Add the roasted squash and onions, along with any oil left on the pan, and stir to coat.
Pour in the chicken stock and simmer over medium-high heat for 5 minutes. Carefully transfer everything to a large high-powered blender. You can process in batches, if needed. Add 3-5 roasted garlic cloves (to taste). Secure the lid on the blender and carefully blend. If you have Blendtec, blend on soup setting. Avoid too much power or pulsing as it could explode out of the blender. Once very smooth, transfer back to the stock pot and set to medium heat.
Stir in the maple syrup and heavy cream. Adjust seasoning with salt and pepper. Serve with toasted pepitas.
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Notes
Note 1: If you buy the pre-cut squash that comes in 16-ounce bags, you'll need 1-1/2 bags.Note 2: Use a heavy and large yellow onion, around 14 ounces in size.Note 3: Check the list below for non-dairy, vegetarian, and vegan variations.
Non-Dairy: Use coconut milk instead of heavy cream for a dairy-free option.
Vegan: Substitute coconut milk for the cream and vegetable stock for the chicken stock.
Vegetarian: Swap the chicken stock with vegetable stock.
Storage: Soup lasts 4-5 days with chicken stock or 1 week with veggie broth. Reheat in a pan over medium-low, stirring occasionally. Freeze in an airtight container for up to 3 months; thaw overnight in the fridge.