Heat oven to 425°F and arrange a rack in the middle.
Line a baking sheet with parchment paper. Place the butternut squash cut-side up on the baking sheet. Melt 1 tablespoon of butter and brush it over the tops and insides of the squash halves. Season generously with salt and pepper. Roast until knife tender, about 50 minutes to 1 hour.
When the squash is cooked, cool it until you can handle it, then scoop out the flesh with a large spoon. Place in a blender and puree. Discard the skins.
In a large heavy saucepan over medium-high heat, melt butter. Add pumpkin seeds, almonds, and onion, and cook until onions are translucent, about 3 to 5 minutes.
Add the butternut squash puree and diced pears and mix well.
Add allspice, star anise, and cloves, then add chicken stock and let it cook over low heat for 20 minutes to allow all flavors to incorporate. Prop a lid over the pan to catch any cooking splashes. Add the Chile de Arbol and heavy cream, and cook for 10 minutes more. Make sure to check that the soup doesn't scorch
Season to taste. Then puree in batches until the soup has a creamy consistency. Add more seasoning if needed. Serve hot.
Garnish with toasted pumpkin seeds, almonds, and minced pear.