Mussels with Chorizo

Unfortunately, this dish is plagued with being totally in fashion. Retro food like moules mariniere is coming right back in, and it seems the incrediblye flavour and versatility of chorizo has long stopped being a secret. But whatever, this is a meal you so want to eat.
1)Mussels have a few rules before cooking: they have to be scrubbed very well (although those little baby shell parasites on them will not come off) and the seaweed feather beard that drifts after each mussel also needs to be ripped off (this is known as debearding). If they remain open at this stage, and don't close after rapping the shell with the side of the sink, they should be chucked. Soak them in the sink for a good while to clear out any grit.
2)Finely slice 3 cloves garlic and 2 small onions or one large one. Slice 200g chorizo into nice slices and cook in a large pan with a little butter until their fat renders out. Cook the onions and garlic in this fat until they're soft and sweet.
3)Make a broth by adding 2 tsp harissa paste, 1 tin of tomatoes and water filled to the brim of the empty can, and 1 1/2 glasses white wine or dry sherry. Bring to the boil, then clamp on a lid and simmer until the bitterness of the wine cooks out.
4)This broth can be kept warm until whenever you need to cook the mussels. It's best to do that between the starter and main course as you don't want cooked seafood sitting around. Bring back up to the boil and throw in your cleaned mussels. Clamp on the lid and steam until they open up, but don't overcook them. It may take 3-5 minutes. Also, any fish that remain closed now should be chucked. Top with freshly chopped parsley, and serve.