Simmer wine, vinegar, sugar, and salt, then pour over shallots and chill for 12 hours.
Marinate the red mullet fillets in garlic, tarragon, and olive oil for at least 1 hour.
Whisk together all the dressing ingredients in a small bowl.
Heat vegetable oil in a deep fryer or deep pan to 180°C.
Coat sliced shallots and garlic in flour and fry for 2 minutes until golden.
Fry the tarragon leaves for 1 minute until crispy and drain on paper.
Coat the fish in flour and deep fry for 7 minutes until crispy and cooked.
Serve fish on warm plates topped with crispy garnishes and dressing on the side.