Preheat the oven to 180°C.
Peal the sweet potatoes then cut them into small chunks. Peel and cut the onion into wedges. Peel the garlic. Cut the pepper into chunks.
Arrange prepared vegetables in a large baking tin, then scatter the cherry tomatoes around them. Tuck the chilli between them (if used). Dust with cumin and dried coriander, season with salt and pepper, drizzle with oil and toss well.
Bake for 20-25 minutes, until the vegetables are tender.
Remove the skin of the pepper, if you like (not essential), then transform everything, including the cooking jus, into a liquidiser and whiz into a smooth, thick cream.
Spoon it into a sterilised jar and keep refrigerated.