What a wonderful exploration of the nuances of flavors. The sweet potatoes, deep-brown caramelized onions, and roasted nuts are all slightly sweet. The flavors meld together beautifully in this delicious and innovative pasta. The tortellini and the sauce can both be prepared a day in advance. Keep both refrigerated; reheat the sauce slowly. The cilantro and potato skins can be fried a few hours before serving, since they do not have to be hot.