Cook the pasta according to the package directions. Drain and set aside.
Heat a large pan over medium heat. Add in the butter and allow it to melt. Cook for another 2-3 minutes until it starts to turn a light brown color. Mix in the sage leaves and reduce the heat to medium low. Cook for about 2 minutes until the sage leaves have toasted and lightly browned. Remove the sage from the pan and set it aside.
Increase the heat back to medium heat. Add in the shallots and garlic. Saute for 2-3 minutes until the shallots turn translucent. Mix in the curry powder, red pepper flakes, and nutmeg. Cook for about a minute until the spices activate and become aromatic. Mix in the pumpkin puree and heavy cream until combined.
Transfer the sauce into a blender and blend until smooth. Pour the sauce back into the same pan and heat it over medium high heat, stirring frequently, until it comes to a bubble. Remove the pan from heat and season with the salt and pepper. Mix in the pasta until well coated in the sauce.
To serve, portion the pasta between bowls. Add a dollop of the whipped ricotta onto the pasta. Drizzle a bit of olive oil on top and add a touch more black pepper and lemon zest. Top with the browned sage leaves and enjoy!