Preheat your oven to 350 degrees Fahrenheit. Cook the pasta in a large pot of salted boiling water until al dente. Reserve one cup of the pasta cooking water, drain the pasta, and then return it to the pot.
While the pasta is cooking, prepare the rest of the recipe. Melt the butter in a small frying pan over medium-high heat. Add the whole sage leaves and cook until they're crispy, about 1 minute. Remove them from the pan and set them aside.
In the same pan, add the pecans and let them toast until they are fragrant, about 5 minutes.
Heat the olive oil in a large pan over medium-high heat. Add the onion and cook till soft, about 5 minutes. Add the garlic and kale and cook until the kale is wilted, about 2 minutes.
In a medium-sized bowl, mix the pumpkin, cottage cheese, sage, black pepper, cayenne, and salt.
Pour the pumpkin sauce over the cooked pasta, add the kale and half of the mozzarella cheese, and mix well. If the pasta seems dry, add some of the reserved pasta water until it is nice and creamy.
Transfer the pasta to a 9x11-inch casserole dish and top with the remaining mozzarella, crispy sage leaves, and buttered pecans. Bake, uncovered, for 25 minutes, or until the pasta is hot and bubbling.
