Bring a large pot of salted water on to a boil.
In a medium bowl, stir together the squash, ricotta, 2 Tbs. Parmesan, 1/4 tsp salt, and nutmeg.
Working with 2 wonton wrappers at a time, top each wrapper with 2 tsp. squash filling. Brush edges of each wrapper with water and fold one corner over filling to meet the opposite corner, forming a triangle. Press down filling to force out any air and seal the edges well. Repeat with remaining wonton wrappers and filling.
In a small skillet melt the butter over medium heat. when the foaming subsides, add the sage leaves and cook, swirling the pan occasionally, until the butter begins to brown, 2 to 3 minutes. Remove from heat.
Add half the ravioli carefully to the boiling water, stirring gently to separate, and cook until they float to the surface, about 3 minutes. Using a slotted spoon transfer to serving plates. Repeat with remaining ravioli. Drizzle with butter-sage sauce. Serve with additional grated Parmesan.