I can't tell you how good this tastes and how easy it is to cook. Soaking the mussels reduces the risk they might carry grit or sand into the sauce.
1 kg fresh mussels
2 tbsp olive oil
1 red onion, halved and finely sliced
500g ripe tomatoes, finely chopped
1 tbsp thyme leaves
500ml beer (lager style)
2 tbsp flat parsley leaves, picked
Soak the mussels in cold water for one hour, changing the water twice. Drain mussels, discarding broken shells. Scrub and pull out beards.
Heat the oil and cook onion for 10 minutes. Add tomatoes, thyme and beer and bring to the boil. Simmer for two minutes, stirring, then add mussels and cover. Cook for two minutes over medium heat, then start removing mussels as they open.
Cover and cook another minute before removing opened mussels. Taste broth and season if necessary, then return mussels to the broth. Scatter with parsley.