In a saucepan, bring to a boil about 1 liter of salted water with the spiked onion. Wash the mussels well under running water, remove the beard and discard any damaged mussels. Place mussels in and steam over low heat, covered, for 3-5 minutes until all mussels are open. Lift out and let cool slightly. Remove mussel meat and keep warm. Finely chop shallots and garlic. Briefly scald tomatoes, peel off skin, remove seeds and cut into cubes. Pit olives and chop finely, as well as the anchovy fillets. Heat olive oil in a saucepan and sauté shallots and garlic. Add the tomatoes, olives and anchovies and continue to sauté for about 2 minutes, then pour in the white wine. Let the sauce boil down for another 4-5 minutes. Mix in mussels and heat again, but do not boil anymore!
Cook pasta of choice and mix with sauce. Season with freshly ground salt and pepper before serving.