Peel the sweet potatoes and cut into cubes. Place on a coated baking sheet or ovenproof dish. Drizzle some oil over it and season with salt. Bake the potatoes in the middle of the oven for 20 to 30 minutes until they are just soft. Remove and reduce the oven temperature to 160 degrees.
Whisk the eggs with the cream, pepper and parmesan, season with salt as required. Pour over the sweet potatoes and sprinkle with sage leaves. Put in the middle of the oven and bake for another 20 to 30 minutes, until the eggs are set. Cut into pieces and serve immediately.
This goes well with grilled chicory rosso or a mixed salad.