Make the dough: In a large bowl, combine the pumpkin puree, flour, egg, salt, and nutmeg. Mix just until a soft dough forms. If it feels very wet, add flour 1 tablespoon at a time until it’s manageable but still tender.
Rest the dough (recommended): Cover and let the dough rest for 10 minutes to hydrate the flour and make shaping easier.
Shape the gnocchi: Divide dough into 4 pieces. On a lightly floured surface, roll each piece into a rope about 3/4-inch (2 cm) thick, then cut into 1-inch (2.5 cm) pieces.
Add ridges: Gently press each piece with the back of a fork (or roll on a gnocchi board) to create ridges. Arrange on a floured baking sheet so they don’t stick together.
Cook the gnocchi: Bring a large pot of well-salted water to a boil. Cook gnocchi in batches. Once they float, cook 30–60 seconds more (about 2–3 minutes total), then lift out with a slotted spoon.
Make the sage butter sauce: While the gnocchi cook, melt butter in a large skillet over medium heat. Add sage leaves and cook until fragrant and the butter is lightly browned. Stir in minced garlic for 30 seconds, then season with salt and pepper.
Toss and serve: Add cooked gnocchi to the skillet and gently toss to coat. Serve hot with Parmesan. Optional: for a crisp finish, pan-fry the boiled gnocchi in butter over medium-high heat until golden on both sides (2–3 minutes per side).