Add the garlic and fennel fronds to the sausage and cook for 3-5 minutes more until garlic is fragrant. Then reduce the heat to low.
Reserve 1/4 cup of pasta cooking water and drain the rest of the pasta.
Add the cooking water and pasta to the skillet and stir to combine. Sprinkle on the cheese and toss again to combine.
Season with pepper and serve (with additional cheese if desired).