Cook the fennel in salted water for 15 minutes, then remove and cut into small cubes. Reserve the cooking water.
Heat the olive oil in a pan over medium heat. Fry the sultanas, pine nuts, fennel and anchovies (cut into small pieces) for 5 minutes. Season with pepper and add the slightly crushed sardines. Keep warm.
Meanwhile, cook the tagliatelle al dente in the reserved fennel water (adding more water if needed). Drain and mix with the sardine sauce.
Serve in deep plates and garnish with a few sprigs of dill.