In a 5-6 quart pot, heat the butter and olive oil over medium heat butter is melted. Add crushed red pepper, let cook a few seconds, and tip in the onion. Sprinkle with the chili powder, salt, black pepper, ginger, and cumin; stir and let cook 5 minutes or until softened. Add whole garlic cloves and cook another minute or two. Pour in broth and water, cover, and bring to a boil. Reduce heat slightly; add diced sweet potatoes. Cook uncovered for 20-30 minutes or until vegetables are tender. Meanwhile, preheat oven to 150 degrees F and place soup bowls on a center rack to warm.