In a medium bowl, mix together the pumpkin puree, ricotta cheese, Parmesan cheese, nutmeg, salt, and black pepper until smooth and well combined.
Lay out the wonton wrappers on a clean, dry surface. Place 1 heaping teaspoon of the pumpkin filling in the center of each wrapper.
Brush the edges of the wonton wrappers with the beaten egg using a pastry brush. Fold the wrappers in half to form half-moons, pressing the edges firmly to seal, ensuring no air bubbles remain.
Bring a large pot of salted water to a boil. Carefully add the ravioli in batches and cook for 3-4 minutes, or until they float to the surface and are tender. Remove with a slotted spoon and set aside.
In a large skillet, melt the butter over medium heat. Add the sage leaves and cook for 1-2 minutes, or until the butter is lightly browned and the sage is crisp.
Stir in the heavy cream and cook for 1 minute, stirring constantly, until the sauce is smooth and slightly thickened.
Add the cooked ravioli to the skillet and gently toss to coat in the sauce. Serve immediately.