Prepare The Sausage
Finely chop the onion. Take the sausage out of the skin and chop it coarsely with a knife. Pour the oil in a big frying pan and let it warm, then add the sausage pieces and sauté it over high heat.

Prepare The Sauce
Add the chopped onion, chilli pepper, fennel seeds and tomato concentrate and let soften for one minute, then add the wine. Let it evaporate, then add the tomato purée, chopped bay leaf, marjoram or thyme, some sugar and salt to taste (but not too much because the sausage is savoury and when the sauce thickens it could taste salty). Let simmer over moderate to high heat for about 30 minutes. If you have more time, cover the pan and let simmer for a longer time. Remember to take the bay leaf and chilli pepper out at the end of cooking.