1.Preheat oven to 240°C. Cook fries according to directions on packet.
2.Meanwhile, melt butter in a large saucepan over medium heat. Stir onion over heat until softened. Stir in garlic and cook until fragrant. Add wine and bring to the boil.
3.Add mussels to pan. Simmer, covered, until mussels open. Stir in tarragon and season. Serve mussels with fries.
Some mussels may not open during cooking. You do not have to discard these; just cook a little longer, or carefully prise the shell open with a knife.Note