Gratin of Mussels and Spinach

• 1.5 kg/3¼ lb fresh mussels
• 1 generous glass of dry white wine

Scrub and debeard the mussels and, with your thumb and forefinger, try to open the shell of each one. If it doesn’t open that’s perfect. If it does open you will find it is full of very, very fine sand which will completely ruin the dish, so you must check each mussel and throw away any open ones. Put the mussels into a large pan, add the white wine (no other liquid), cover with a tight-fitting