Preheat your oven to 400 F (200 C), prick the sweet potatoes all over with a fork and roast on a tray in the oven for 45 minutes until tender. Once roasted, cut the hot potatoes in half and leave them to cool. Scoop out the cooled flesh and place into a food processor, blend until smooth. Add the ricotta, parmesan, salt, pepper, nutmeg and egg then blend again. Add the flour and blend in until just combined. Chill the dough for at least 2 hours before shaping.