Brush the sweet potatoes with a little oil and place along with the garlic on a baking tray. Roast in a preheated oven for 35 minutes (or until tender). Remove from the oven, peel and make the soup.
In a large pot heat up the oil, add the onion, garlic, sweet potatoes and fry for 3 minutes, stirring often. Add the spinach, vegetable stock, pepper to taste, stir, cover and bring to the boil then simmer for 3 minutes. Remove from the heat, puree, adjust the seasoning and serve.
Sweet potato: Use long thin sweet potatoes as they will take less time to roast.
Make ahead: To save time you can prepare the sweet potato and garlic in advance. Simply roast these as per instructions, then allow to cool completely and refrigerate (overnight), covered, until you are ready to make the recipe. Remove the skin just before making the soup.
Storing: Keep leftover soup refrigerated for up to 3 days.
Serving suggestions: Serve with toasted sunflower/pumpkin seeds, a dollop of yogurt, drizzle of balsamic vinegar and oil.
Freeze for up to 3 months.
Preparation time includes the time needed to roast the vegetables.