Serves 4 as a starter or 2 as a main course. Best with the large Spanish mussels — small moules de bouchot should not be wasted on this!
1 kg huge mussels
200g softened butter
2 tbs finely chopped flatleaf parsley
1 large garlic clove, chopped
1 small shallot, finely chopped
pinch nutmeg
black pepper (no salt, the mussels are salty)
25 g fresh white breadcrumbs
To make the butter, mash it with the garlic, shallot, parsley, pepper and nutmeg, and set aside.
Wash and debeard the mussels, throwing away any broken or open ones. Warm either one large gratin dish, or 2/4 individual ones. Just before cooking, give the mussels a last rinse, then put them in a large pan without any added water and cook covered over a high heat for 3-4 minutes, shaking vigorously a couple of times, just until they open — stop cooking as soon as they do (and as usual throw away any that didn’t open). Quickly take them out with a slotted spoon, remove and discard the empty half of the shells, put the mussels in their shells in the gratin dish(es), and cover loosely with foil.
Preheat the oven to gas 8/200C. Pour the liquid from the mussels through a muslin-lined sieve (to get rid of any sand) into another pan, and boil down rapidly until you have a small amount of syrupy liquid. Beat this into the butter. Now put a teaspoon of butter into each shell, and sprinkle breadcrumbs over the whole lot. Put uncovered into the oven for 4 or 5 minutes, just long enough to melt the butter and toast the breadcrumbs. Serve immediately, with lots of bread to mop up the juice.
NB: you could do this under the grill as well.