In a large mixing bowl, combine pumpkin purée, egg, cheese, and salt.
Gradually add flour and mix until a soft, slightly sticky dough forms.
Dust your work surface with flour. Divide the dough and roll into ropes about 1 inch thick.
Cut each rope into 1-inch pieces. Use a gnocchi board or fork to create ridges, if desired.
Line a tray with baking paper and place the gnocchi pieces on it.
Bring a large pot of salted water to a boil. Add gnocchi in batches and cook until they float (2–3 minutes).
Use a slotted spoon to remove them and set aside.
In a skillet, melt butter over medium heat. Add sage leaves (and garlic, if using) and cook until fragrant and butter turns golden brown.
Toss the cooked gnocchi in the sage butter sauce.
Optional: Add fresh spinach and stir until wilted.
Serve warm, topped with extra grated parmesan cheese.