Prepare the vegetables. Peel and cube the butternut squash and sweet potatoes. Slice the onion into half moons and smash and peel the garlic cloves.
Season and roast. Spread the vegetables on a roasting pan. Drizzle with olive oil and season with cinnamon, cumin, chili powder, salt, and black pepper. Roast at 400°F until tender, about 30 minutes.
Simmer the soup. Transfer the roasted vegetables to a large pot. Add vegetable broth until the vegetables are just barely covered. Bring to a boil.
Blend until smooth. Use an immersion blender to blend the soup until creamy and velvety.
Add the cream. Stir in the heavy cream. Taste and adjust the salt, pepper, cumin, chili powder, or crushed red pepper as desired.
Garnish and serve. Ladle into bowls and finish with a swirl of heavy cream, fresh sage leaves, and salted pepitas. Add a pinch of crushed red pepper or chili powder if desired.