vegetable oil, for deep-frying
2 tsp milk
80g rice flour
25g panko (Japanese-style) breadcrumbs
4 ling fillets, skin removed, pin-boned
4 brioche buns, cut in half horizontally
8 baby cos (romaine) lettuce leaves
2 whole pickled onions, sliced into rings
2 pickled cucumbers, thinly sliced lengthways
100g tartare sauce
1. Half-fill a medium saucepan with vegetable oil and place over high heat (see note). Heat the oil to 180°C (350°F) – check with an oil thermometer. (For a guide to testing the oil temperature without a thermometer, see note.)
2. In a large, shallow bowl, whisk the egg and milk together to make an egg wash. Place the rice flour in another bowl and the panko breadcrumbs in a third. Dust each ling fillet in the rice flour first, then dip it in the egg wash and, lastly, the breadcrumbs.
Tap off any excess crumbs and lower the ling fillets carefully into the hot oil. Fry the ling for about 2 minutes, or until crisp and golden. Remove from the saucepan and drain on a baking tray lined with paper towel.
3. Place the bottom half of each brioche bun on a tray. Add two lettuce leaves to each and top with the fried fish. Add the pickled onion rings, pickled cucumber and tartare sauce, then place the other brioche half on top and serve.