Cut the squash in half, length-wise and scoop out the seeds and veins. Place each squash half face down on a baking sheet (you can use a piece of parchment paper if you'd like cleanup to be easier). Place in oven and roast for 60 minutes or until all flesh is easily pierced with a fork.
Cut the cauliflower head into florets and toss with avocado oil, salt and pepper. Place florets onto a baking sheet and place in the oven with the cauliflower. Roast for 45 minutes or until cauliflower starts to get golden brown.
Nearing the end of the roasting time, dice the yellow onion.
Place a large soup pot onto the range on medium to medium-high heat and add the coconut oil.
When the coconut oil is shimmering and hot, add the onion. Sautée for 5 minutes of until the onions are translucent.
Scoop the meat out of the squash and add to the sautéed onions.
Add the roasted cauliflower to the onions and squash. Stir to incorporate.
Add 8 cups of vegetable broth and simmer over medium heat for 30 minutes.
After the soup simmers, working in batches put soup into a blender (with a vent) or a food processor and purée until creamy.
Add puréed soup back to pot and season to taste with salt and freshly ground pepper.
Serve in bowls with dairy free vegan sour cream or crème fraîche.