Melt butter and oil in large pot over medium heat; add onion and cook until softened, about 5-6 minutes; stir in squash and cauliflower, broth, thyme. Bring to a simmer and cook covered until the squash and cauliflower are tender.

Puree soup using a hand blender or carefully in batches using a regular blender.

*at this point you can save the soup for future use*

Mix in the heavy cream and bring to a low simmer and then remove from heat. Season with salt and pepper; add nutmeg. Serve Warm.