Heat some olive oil in a frying pan and add the sausages. Fry over a medium heat for a few minutes until browned all over. Remove from the pan, leave to cool slightly and then cut into bite sized pieces.
Add the garlic to the same pan and gently fry for a minute or two before adding the fennel and chilli. Add the balsamic and use it to deglaze the pan. Add the tin of tomatoes, tomato puree and salt and pepper. Return the sausage pieces to the pan and allow this all to bubble over a medium heat for 15-20 minutes, stirring occasionally, until the sauce is reduced to quite a thick consistency.
Meanwhile, cook the pasta until al dente.
When the pasta is ready, drain it and add it to the sauce with the herbs if using. Mix well through and grate over fresh parmesan to serve.