Preheat oven to 180°c
To make the sweet potato puree: In a saucepan, cover potatoes with water and bring to a boil. Cook until sweet potatoes are tender when the top of a knife is inserted, for about 15-20 minutes. Reserving some of the water, drain the pan and place sweet potato in a food processor. Puree until smooth, adding the water if necessary. Leave to the side.
Add oil to a pan with the onions and sage leaves. Cook until the onion is translucent, but not brown. Add the garlic and cook, stirring, for 30 seconds. Remove sage leaves.
In an ovenproof dish add the onion, garlic and rice, pouring over the vegetable stock and sweet potato puree, stir well. Bake for 30-40 minutes, depending on how you like it. Make sure to stir halfway through.
Stir well. Season to taste with salt and pepper. Garnish with fresh sage leaves and pomegranate seeds.