When sausage is brown, add fennel seeds and mix. Keep warm.
Beat the eggs in a medium bowl with wire whisk until slightly thick.
Cook pasta in a separate pot of boiling water until al dente (about 8-10 minutes). Drain well and return pasta to pot.
Add the butter and toss well. Add the beaten eggs and keep tossing. Add the sausage with fennel, the cheese and salt to taste. Top with parsley and serve immediately.