Roasted sweet potatoes, bell peppers, tomatoes, onion, and garlic give this easy vegetarian sweet potato soup deep flavor and a silky texture without heavy cream. Finish each bowl with tangy Greek yogurt, parsley, olive oil, and Aleppo pepper.
Get ready. Preheat the oven to 425°F with a rack in the center. Line a baking sheet with parchment paper.
Prepare the vegetables. Spread the sweet potatoes, bell peppers, red onion, tomatoes, and whole, unpeeled garlic cloves across the prepared baking sheet in a single, even layer. Drizzle with the olive oil and sprinkle with the salt.
Roast the vegetables. Roast until the vegetables are completely tender and lightly browned, about 35 minutes. Meanwhile, warm the vegetable broth.
Blend the soup. Squeeze the roasted garlic cloves from their skins. Carefully transfer the roasted vegetables to a blender and add one-third of the warm broth. Pulse, then purée until smooth, gradually pouring in the remaining broth.To use an immersion blender, transfer the vegetables to a soup pot. Add one-third of the warm broth and purée, gradually streaming in the remaining broth as you blend.
Garnish and serve. Divide the soup among four bowls. Garnish each serving with Greek yogurt, a drizzle of olive oil, and chopped parsley. Add Aleppo pepper or crushed red pepper flakes, if you like, and serve with crusty bread.
Blender safety: Be careful when blending hot soup. Remove the center cap from the blender lid so steam can escape, then cover the opening loosely with a kitchen towel. Work in batches if necessary.
Vegan option: Use plain plant-based yogurt in place of Greek yogurt.
Storage: Refrigerate the ungarnished soup in a covered container for 3 to 4 days or freeze it for 2 to 3 months. Reheat it in a saucepan, adding vegetable broth or water if it has thickened. Add the yogurt and other garnishes just before serving.