3 medium sweet potatoes OR beets , roasted and peeled ¾ cup ricotta cheese ½ cup grated Parmesan Reggiano cheese, plus more for garnish 1 egg ¾ tsp. salt, plus more for salting water ¼ tsp. nutmeg 2½ cups flour, plus more for dusting sauce 4 tablespoons butter 1 teaspoon lemon juice 1 tablespoon chopped fresh thyme or another fresh herb such as rosemary or oregano
In a large mixing bowl, mash potatoes until no large chunks remain. Add ricotta, Parmesan, egg, nutmeg and salt and continue mashing until well combined. Fold 2 cups of flour gently into the sweet potato mixture until well combined. The dough should be slightly sticky. To test, take a small handful of the dough and roll it into a log on a well-floured surface. If the dough continued to stick, add 2 more tablespoons to the dough and try again. Continue to add 2 tablespoons at a time until the dough does not stick when rolled. Let the dough sit for about 30 minutes.
Line a sheet pan with parchment paper and sprinkle with flour. Taking a large handful at a time, roll dough on a well-floured surface into logs about ½ inch in diameter. With a knife cut, the logs into ½ inch pieces. Add more flour to the surface as needed. Place cut gnocchi on the sheet pan and dust with flour. Continue to work in batches until all of the dough is rolled and cut.
Place gnocchi in batches into boiling water. Reduce heat so that the water is at a low, rolling boil. After gnocchi starts to float, at about 2–3 minutes, cook for 1 minute more. Using a strainer, take the gnocchi out of the water and place in a serving bowl and begin another batch.
Meanwhile, melt butter in a medium pan. Add the thyme and cook until fragrant, about 2–3 minutes. Add lemon juice and salt and cook until butter just begins to brown, about 2 minutes more. Pour sauce over the gnocchi and serve with a sprinkle of Parmesan cheese.