How to Make It
Heat the oven to 400°. Bake the sweet potatoes until soft, about 11/4 hours. Turn off the oven. Cut the sweet potatoes in half lengthwise and put the halves back in the still warm oven for 10 minutes to dry.
In a food processor, pulverize the amaretti. Peel the sweet potatoes and add the flesh to the food processor. Process until the mixture is smooth. Scrape the filling into a bowl and stir in 1/4 cup of the Parmesan, the parsley, nutmeg, 1/4 teaspoon of the salt and 1/4 teaspoon pepper. Cool to room temperature.
Roll, fill and cut the ravioli. They should be 2-inch squares with about 3/4 teaspoon of filling in each one.
In a large pot of boiling, salted water, cook the ravioli until just done, about 7 minutes. Drain.
In a large frying pan, melt the butter and the remaining 1/2 teaspoon salt over moderate heat. Cook until the butter turns golden brown, about 2 minutes. Add the ravioli, the remaining 1/4 cup Parmesan and a large pinch of pepper. Toss and serve with extra Parmesan.
Working with a third of the dough at a time, roll it out to less than 1/16 inch thick by hand or with a pasta machine. If rolling the dough by hand, cut it into 5-inch- wide strips. If using a pasta machine cut the length of dough crosswise in half.
Arrange one strip of dough on a floured work surface. Drop 3/4- teaspoon mounds of filling in two rows, about 2 inches apart, down the length of the dough. Drape the second sheet of dough over the filling. Firmly press around each mound of filling, taking care to press out any air that may be trapped inside.
With a fluted pastry cutter, cut the ravioli into 2-inch squares. Firmly press around the edges to seal them. Alternatively, fill and cut the ravioli using a ravioli mold and following the manufacturer's instructions. Put the finished ravioli on a baking sheet dusted with flour. Continue with the remaining dough and filling.