For the white wine shallots, put the shallots in a bowl. Put the white wine, white wine vinegar and sugar in a saucepan and bring to a simmer over a medium heat and add a pinch of sea salt. Pour the hot pickling liquor over the shallots, make sure they are submerged and leave to cool. Pour into an airtight container and leave in the fridge for 12 hours before using. Store the shallots in a sterilised jar in the fridge, they will keep for 3 months.
For the red mullet, put the fish in a shallow dish. Mix the garlic, tarragon, olive oil and a pinch of sea salt together in a bowl. Spoon over the fish, cover and leave to marinate in the fridge for at least 1 hour.
For the dressing, mix all the ingredients together in a bowl.
Heat the vegetable oil in a deep-fat fryer to 180C. Alternatively, heat it in a deep heavy-based frying pan until a breadcrumb sizzles and turns brown when dropped into it. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
For the garnish, put the gluten-free flour on a plate and coat the shallots and garlic in it, tapping off any excess. Deep-fry the shallots and garlic in the hot oil for 2 minutes, until golden brown and crispy. Remove, drain on kitchen paper and season with salt.
Deep-fry the tarragon for about 1 minute, until crispy, taking care as the oil will split a little. Remove and drain on kitchen paper.
To cook the red mullet, scrape off any marinade, then dip the fish in the flour to coat and tap off any excess. Carefully lower the fish into the hot vegetable oil and deep-fry for 6-7 minutes, until cooked and crispy. Carefully lift out the fish and drain on kitchen paper then season all over with salt. (If your deep-fat fryer isn’t big enough, cook the fish in two batches, keeping the first batch warm in an oven heated to 100C/80C Fan/Gas ¼ while the second batch is cooking).
Serve the mullet on a warm plate, garnished with the crisp tarragon, shallots and garlic, with the dressing in a bowl on the side.