This delicious fall soup is inspired by one that I had many years ago at California Cafe in Los Gatos. Sadly the restaurant has been closed for years, but I loved this soup so much that the chef kindly brought me a copy of the recipe with his handwritten notes on it to our table and I've been making it ever since. Fast forward about 15 years - one of my jobs during my time as an intern at Flea Street Cafe in Menlo Park was to make 16 quarts of vegan Butternut Squash Soup multiple times a week. I combined many ingredients and techniques from both versions, and this is my favorite way to make it. Due to the addition of cream at the end as well as hints of maple syrup and cinnamon, is a perfect soup to have a cup or small bowl of at the beginning of a meal. It's also great as a soup + salad or soup + panini combo.
Preheat oven to 300°. Rinse the outside of the squash (it will sit in liquid while it cooks and you will use in the soup, so you want a clean squash). Cut squash ends off, then in half lengthwise, and remove seeds. Place halves in a roasting pan, cut side up. Add thyme sprigs, bay leaf, brown sugar and kosher salt to the top and cavity of the squash. It's ok if some falls off and into the pan. Add water to the bottom of the pan and cover tightly with a sheet of parchment paper, followed by a sheet of heavy aluminum. Place in the oven and cook for 1 hour.
Meanwhile, in a large heavy pot, melt butter and olive oil over low heat. Add onion, celery, carrot, garlic, kosher salt and black pepper. Cook over low heat, stirring occasionally, about 20-30 minutes total. You are looking for very soft vegetables and only the slightest hint of color. Turn off the heat while the squash finishes cooking.
When the squash has cooked for an hour, remove from the oven and carefully take the parchment and foil off and let the squash cool a few minutes. Be sure to save the liquid in the pan; you should have a little less than 2 cups.
Scoop out the flesh and add it directly to the pot with the vegetables. Add pumpkin puree, stock and flavorful cooking liquid from roasting pan to the pot with the vegetables and bring to a boil, then cover, lower the heat and simmer for 30 minutes.
Remove from heat and add heavy cream, maple syrup, and cinnamon. Carefully blend mixture with an immersion blender directly in the pot. For the most smooth texture, use a high speed blender such as a Vitamix, blending in batches and returning soup to the pot to reheat.
Top each serving with any of the following toppings: a spoonful of crème fraîche, freshly grated nutmeg, finely chopped chive, a drizzle of pumpkin or olive oil, toasted/spiced pepitas, coarse flake salt