In large bowl, combine pumpkin and butter. In another bowl, combine flour, yolk, salt and nutmeg. Add to pumpkin and butter and knead into soft dough adding more flour 1 tablespoon at a time if needed until no longer sticky. Divide into 4 sections and roll into strips about 3/4-inch thickness. Cut into 3/4-inch pieces, rolling each piece against the tines of a fork to create ridges. Repeat with remaining dough. In large pot, bring 6 cups of water to boil and add a generous amount of salt (so it tastes like the sea.) Cook gnocchi in 2 batches until pieces float, about 2 minutes. Remove with slotted spoon to warmed bowl. Meanwhile, melt butter in a skillet over medium heat until it starts to deepen in color. Add hazelnuts, sage and salt and cook 1 minute more. Remove from heat and add a couple of squeezes of lemon juice. Add gnocchi to pan and toss to coat then top with pecorino or parmesan cheese and serve.