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, covered (for up to 2 days), until you are ready to make the recipe. Remove the skin just before you make the recipe.
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.