Like the potato gnocchi, these sweet-potato dumplings can be boiled without the step of rolling them down the tines of a fork, either as is or just put a thumb indentation in each one instead.
Scoop the cooked sweet-potato flesh out of the skin and mash it with a fork, or put it through a potato ricer or food mill. Toss the potatoes with the flour and salt in a bowl with your hands. Use a light touch.
Make a well in the center of the sweet potato mixture and put the egg in it. Gradually incorporate the potato mixture into the egg to make a dough that comes together. Roll dough into 1-inch-thick logs and cut 1-inch pieces off the logs.
For the traditional indentations, roll each piece down the tines of a floured fork and flick it off with your thumb.
Bring a pot of salted water to a boil, add the gnocchi, stir, and then cook until they float to the top, about 5 minutes.
Drain the gnocchi and put them in a serving dish. Toss the gnocchi with the melted browned butter and sage to coat. Sprinkle the Parmesan cheese over them and serve immediately.
Substitution. . . . . . . . . . . . . . . . . . . . . . . . . .
Gnocchi can be made with other things besides potatoes and sweet potatoes. Butternut squash is a good one. Spinach can be added to regular potato gnocchi, and ricotta cheese is another delish gnocchi.