2 (1¼ lbs) russet potatoes
1 (¾-lb) sweet potato
1 large egg
½ teaspoon nutmeg, freshly grated
Freshly ground pepper
â…“ cup grated Parmigiano-Reggiano plus more for serving
1½ to 2 cups all-purpose flour plus more for dusting
½ stick unsalted butter
1 cup sage leaves (from 1 bunch)
Preheat oven to 450Â°F. Pierce russet and sweet potatoes in several places with a fork, and then bake until just tender, 45 minutes to 1 hour. Cool potatoes slightly, then peel and force through ricer into sheet pan, spreading in an even layer. Cool potatoes completely. Lightly flour 2 large baking sheets or line with parchment paper. Beat together egg, nutmeg, 1 tsp salt, and pepper in a small bowl.
Gather potatoes into a mound in sheet pan, and form a well in center. Pour egg mixture into well, then knead into potatoes. Knead in cheese and 1½ cups flour, then knead, adding more flour as necessary, until mixture forms a smooth but slightly sticky dough. Dust top lightly with some of flour. Cut dough into 6 pieces. Form 1 piece of dough into a Â½-inch-thick rope on a lightly floured surface. Cut rope into ½-inch pieces. Gently roll each piece into a ball and lightly dust with fl our. Repeat with remaining 5 pieces of dough. Transfer gnocchi as formed to baking sheets.
Bring large pot of water to boil; add salt and return to boil. Working in batches, boil gnocchi until tender, 5 to 6 minutes. Transfer gnocchi to clean rimmed baking sheet.
Melt butter in heavy large saucepan over medium-high heat. Cook until butter solids are brown and have toasty aroma, swirling pan occasionally, about 5 minutes. Add chopped. Turn off heat. Season sage butter generously with salt and pepper.
Transfer half of sage butter to large skillet set over medium-high heat. Add half of gnocchi. SautÃ© until gnocchi are heated through, about 6 minutes. Repeat with remaining sage butter and gnocchi.
Divide gnocchi and sauce among shallow bowls. Garnish with sage leaves.