Mix the pumpkin puree, ricotta, egg, salt, and nutmeg in a large bowl until smooth.
Add the flour gradually and stir until a soft dough forms. Turn the dough out onto a floured surface and knead gently for about one minute until it holds together.
Divide the dough into four pieces. Roll each piece into a long rope about 3/4 inch thick, then cut into 1-inch pieces. Place the pieces on a floured baking sheet.
Bring a large pot of salted water to a boil. Drop in the gnocchi in batches and cook until they float to the surface, about 2 to 3 minutes. Remove with a slotted spoon and set aside.
Melt the butter in a large skillet over medium heat. Add the sage leaves and cook, swirling the pan, until the butter turns golden brown and the sage crisps, about 3 to 4 minutes.
Add the cooked gnocchi to the skillet and toss gently to coat. Season with black pepper, then sprinkle with Parmesan before serving.