Bake the peeled sweet potatoes in the oven for about 1 hour at 200 ° C.
Finely chop the onions, sauté them in the margarine until they are soft, then add the brown sugar, maple syrup and cinnamon and let it caramelize.
When the potatoes are tender, peel them and place in a bowl. Pour the onion sauce over it and serve sprinkled with a little brown sugar and freshly ground black pepper.