• Wash and debeard the mussels. Not done it before, take a look here: https://www.epicurious.com/expert-advice/how-to-clean-and-debeard-mussels-article
• Discard any mussels that are open.
• Place mussels in a large deep pan over a low flame. Pop on a lid and give it at least 4-5 mins until majority are open. Give a shake regularly.
• When opened, remove them from heat, take the half shells off. Discard any that are still closed.
• Strain mussel juices from the pan. If they are from the supermarket they will be grit free, if fresh from the sea you will need to strain the juice through a clean muslin/tea towel.
• Keep the mussels, each remaining in their half shell, warm in the oven (low heat).

Now for the sauce

• Melt the butter in a pan, stir in flour over a low heat.
• Add garlic, tarragon, wine and some of the mussel liquor, enough to produce a thin sauce. After 5-8 mins add the gin. Allow to simmer for another 5mins or so.
• Season, go easy on the salt if your mussels are fresh. Add the egg yolk to bind the sauce. Add the lemon juice.
• Put the mussels into the sauce, serve with French fries. Bon Appetit!