In a 5+ qt pot, heat two tablespoons of olive oil over medium heat. Add in the sliced onions and sauté until softened and fragrant, about 5 minutes. Add in the minced garlic and sauté for another 30 seconds or so, stirring constantly to prevent burning.
Next, add in the cauliflower florets, white wine vinegar, balsamic vinegar, maple syrup, and pumpkin pie spice. Sauté for an additional 5 minutes, coating the cauliflower well.
Add in the pumpkin puree, vegetable broth and water and stir to combine. Bring the soup to a boil, then reduce the heat slightly, add the lid, and allow to simmer for 20-25 minutes, or until cauliflower florets are fork tender.
Turn off heat and blend your soup until smooth with an immersion blender. Alternatively , carefully transfer soup in batches to a blender and blend until smooth. Be sure to leave ample room in a blender as heat expands.
Optional: Stir in a corn starch slurry to thicken (Mix 2 tablespoons cornstarch with 4 tablespoons water). If you do not mix the corn starch with water beforehand, it will clump in the soup.
Season with salt and pepper to taste and serve immediately.
Storage Instructions:
Allow to cool completely, then store leftovers in an airtight container in the refrigerator for up to three days or freeze for up to 3 months.
Notes
Slow cooker method: Simply add all of the ingredients, except for the cornstarch to the slow cooker bowl, with the sliced onions on the bottom. Do not stir - this will allow the onions to caramelize. Cook on low for 8 hours for best flavor, or on high for 4. After cooking, blend until smooth with an immersion blender and then stir in cornstarch slurry, if desired.
If you want to make this recipe with fresh pumpkin, I recommend substituting the pumpkin puree with 4 cups of cubed sugar pie pumpkin. Add the cubed pumpkin in at the same time as you would the cauliflower florets and simmer the cubes in the soup for the 20-25 minutes.
You can also substitute the pumpkin with 4 cups butternut squash.
This soup freezes beautifully! Allow it to cool completely before storing, then store in a freezer safe vessel. To thaw, transfer to the refrigerator for 24-48 hours then simply reheat. Any separation is natural - just stir to combine.