Sauté Aromatics: Melt butter in a large pot over medium heat. Add chopped onion, minced garlic, salt, and pepper. Cook until onions are browned (5-7 minutes).
Toast Spices: Stir in curry powder, cumin, and cinnamon. Cook for 1-2 minutes, then increase heat to medium-high.
Add Liquids and Veggies: Pour in water and chicken broth, bringing to a boil. Add sweet potatoes and cauliflower, reduce heat, and simmer for 25-30 minutes until vegetables are tender.
Blend Soup: Use an immersion blender to puree the soup until smooth. Add more water if it's too thick.
Final Heat: Cook for an additional 3-5 minutes until heated through.