This recipe was provided by Atlantic Gin. Inspired by La Mouclade by Alan Davidson.
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).
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!