In a large skillet, heat the oil over medium-high heat. Add the sausage and cook, stirring and breaking up the meat, until it’s browned on all sides, 7 to 10 minutes. Remove the sausage with a slotted spoon and transfer it to a plate.
Add the garlic to the same skillet and sauté for 2 minutes, until light golden. Add the shallot and cook for 2 minutes more. Add the red pepper fakes, if using, and cook until fragrant, about 30 seconds. Add the fennel and salt and sauté until the fennel has softened, 3 to 5 minutes. Add the stock and cook a few minutes more.
Bring a large pot of salted water to a boil over high heat. Add the kale to the boiling water and blanch it for 2 to 3 minutes. Using a slotted spoon, remove the kale and add it to the skillet, along with the sausage. Return the water to a boil and add the pasta. Cook according to the package directions until al dente.
Drain the pasta into a colander, making sure to reserve 1 cup of the cooking water. Add the pasta to the skillet and cook it with the sausage and kale over low heat for 1 to 2minutes. If the pasta is dry, moisten it with the reserved pasta water, adding ¼ cup at a time. Check and adjust the seasoning.
Finish the pasta with grated cheese and freshly cracked pepper. Serve immediately
