Start by peeling and chopping the sweet potatoes and butternut squash into uniform pieces, ensuring even cooking. Sauté chopped onion and minced garlic in olive oil in a large skillet or directly in the slow cooker until fragrant and translucent, about 5 minutes.
Add the chopped root vegetables to the slow cooker along with the sautéed onion and garlic. Pour in vegetable broth, then sprinkle in ground cinnamon, salt, and pepper to taste to build layered flavors.
Set the slow cooker to low and cook for about 6 hours, until the vegetables are tender and easily mashable. The house will fill with a warm, inviting aroma during this time.
Once cooked, carefully transfer the mixture to a blender or use an immersion blender directly in the slow cooker. Puree until smooth and creamy, with a vibrant orange hue. If the soup is too thick, stir in additional warm broth or water to loosen it.
Taste and adjust seasoning with salt and pepper as needed. Reheat gently, stirring occasionally, until steaming hot.
Serve the soup in bowls, garnished with freshly chopped thyme or parsley for a burst of fresh flavor. Pair with crusty bread for a cozy, complete meal.