In a large saucepan melt the butter and then add the garlic, lemon zest and rosemary. Cook gently for 3-4 minutes over a medium heat or until fragrance of the garlic wafts up to your nose, now add half of the parsley, the chilli and the mussels and stir. Then add the lemon juice and the wine, put the lid on and bring the wine to the boil.
Cook for a couple of minutes, or until the mussels have opened, stir in the rest of the parsley, a pinch of salt and some olive oil and remove from the heat. Discard any mussels that have not opened.
Pour the mussels into a large bowl and serve with crusty bread.