Put a large pan of well-salted water on to boil, so that you’re ready to cook the pasta while the sauce is coming together
Trim the fennel, removing the tougher outer layer or two, then slice thinly. Heat the oil in a large frying pan over a medium heat. Add garlic and fennel and sauté gently for about 10 minutes until fennel is tender.
When the fennel is almost cooked, add the pasta to the pan of boiling water and cook until al dente.
Add the rocket to the fennel and stir until wilted, then add the lemon zest and sour cream. Stir well until the sour cream coats the vegetables, then add salt and pepper to taste.
Drain the pasta, toss with the fennel mixture and serve straight away, with grated cheese.