Cut the fish into 2.5cm chunks, season with sea salt and black pepper, squeeze over the juice of 1 lime and set aside for 10 minutes.
Pick and finely chop most of the fresh coriander leaves for the dip (reserving some for a garnish) and stir through the yoghurt in a small bowl.
Peel and crush the garlic, and add to the yoghurt along with the zest of the clementine half. Season to taste and set aside.
Crush the chipotle flakes using a pestle and mortar. Transfer to a large, shallow dish with the ground coriander, cornflour and a pinch of salt, then mix well. Pour the milk into a separate bowl.
Pour the oil into a large, thick-bottomed saucepan to a depth of around 6cm (it should be no more than two-thirds full). Heat it to 170ºC/325ºF (if you don’t have a thermometer, dip the end of a wooden spoon in the oil – if it starts bubbling rapidly around the spoon, it’s ready).
Slice the clementines as thinly as you can – about 1mm. This can be fiddly, so don’t worry about getting perfect rounds.
Pat the fish and clementine slices with kitchen paper to soak up any excess juice. Coat them in the cornflour, then dip briefly in the milk before coating again in flour, shaking off the excess.
Deep fry the fish and clementine in batches for 2 to 3 minutes, or until golden.
Drain on kitchen paper and scatter with salt, chipotle and the reserved coriander. Serve immediately with the dip and the remaining lime cut into wedges.