1. In a large frying pan, heat half the oil over medium-high heat. Add the sausage and cook, stirring and breaking up the meat, until it’s browned and cooked through. Remove the sausage with a slotted spoon and transfer it to a plate.
2. Add the garlic, shallot and chilli flakes to the same pan and cook, stirring, for 1 minute until fragrant. Add the fennel, cook, stirring, until the fennel has softened. Add the stock and cook a few minutes more.
3. Bring a large pot of well salted water to a boil over high heat. Add the cavelo nero to the boiling water and blanch it for 1 minute. Using a slotted spoon, remove the cavelo nero and add it to the fennel mixture in the frypan. Return the water to a boil and add the pasta. Cook until al dente.
4. Drain the pasta into a colander, making sure to reserve ½ cup of the cooking water. Add the pasta and the sausage to the frying pan and stir over low heat until combined. If the pasta is dry, moisten it with the reserved pasta water, adding ¼ cup at a time. Check and adjust the seasoning.
5. Serve the pasta with grated parmesan and freshly cracked pepper. Serve immediately.