Preheat the oven to 425°F (218°C).
On a large baking sheet, toss the butternut squash and pumpkin with the oil and sea salt. Roast the squash and pumpkin for 30 minutes, until they are fork tender.
Meanwhile, melt the butter in a large soup pot over medium heat. Add the onion, carrot, sweet potato, and a large pinch of sea salt.
Cook the vegetables for 10 minutes, until the veggies are soft and slightly caramelized. Add the garlic and pears and cook the mixture for 3 to 5 minutes.
When the squash and pumpkin are done roasting and are cool enough to handle, use a knife to slice the skin away from the pumpkin. Discard the skin.
Add the broth, milk, and butternut squash and pumpkin to the soup pot. Bring the soup to a simmer. Turn the heat off and puree the soup using an immersion blender. (Alternatively, you can blend the soup in a countertop blender, working in batches if necessary.) Stir in the sugar (if using), sea salt, and black pepper.
This soup will last for 5 days in the refrigerator. To freeze the soup, let it cool to room temperature, and then store it in freezer-safe containers in the portion sizes that you want.