Ravioli Filled with Sweet Potato

Ravioli filled with the sweet local pumpkin is a specialty of Ferrara in Emilia-Romagna. When my mother first tried the recipe in the U.S. she found that the orange-fleshed sweet potato available here was the closest equivalent to the Italian pumpkin. I have found that butternut squash is also an acceptable alternative although the sweet potato is still my favorite. The sauce I like best to serve them with is a butter and sage sauce, but plain butter and Parmigiano cheese works very well to