Wipe the pan and return it to the heat. Melt the butter and add the saffron, crème fraîche, the mussel liquor, and season. Bring to the boil and simmer for a couple of minutes, then return the spinach and the mussels. Cook for a minute to warm the mussels through, and serve immediately in warmed bowls with crusty bread.
Jeannie Chesterton trained at Le Cordon Bleu in London. For over 30 years she has lived in Andalucia with her husband, Sam. They are co-authors of the Buenvino Cookbook: Recipes from our Farmhouse in Spain (£20, Bene Factum).