In a large bowl, combine pumpkin puree, flour, egg, salt, nutmeg, and Parmesan cheese (if using). Mix until a dough forms. The dough will be slightly sticky.

Turn the dough out onto a lightly floured surface and knead for 2-3 minutes, adding more flour as needed to prevent sticking. The dough should be soft but not too sticky.

Roll the dough into a long rope, about 1 inch thick. Cut the rope into 1-inch pieces. Using a fork, gently roll each gnocchi piece over the tines to create ridges.

Lightly flour a baking sheet and place the gnocchi on it. While the gnocchi are resting, prepare the sauce.

In a large skillet, melt butter over medium heat. Cook until butter is browned and nutty, about 3-5 minutes. Add sage leaves and cook for 30 seconds until fragrant. Remove from heat and set aside.

In the same skillet, heat olive oil over medium heat. Add minced garlic and cook for 1 minute, until fragrant. Stir in diced tomatoes (undrained) and bring to a simmer.

Reduce heat to low and simmer for 10 minutes, allowing the sauce to thicken slightly. Stir in heavy cream, browned butter and Parmesan cheese. Season with salt and pepper to taste.

Bring a large pot of salted water to a boil. Gently add the gnocchi to the boiling water and cook for 2-3 minutes, or until they float to the surface. Remove the gnocchi with a slotted spoon and add them to the sauce.

Toss to coat the gnocchi in the sauce. Serve immediately, garnished with fresh sage leaves (if desired).