To make the deep-fried monkfish cheeks, whisk 200g/7oz flour, yeast, beer and sparkling water in a bowl until you have a loose batter. Leave to stand for 30 minutes until foaming.
Meanwhile, to make the mussels, if any mussels are open, tap them lightly on a hard surface. If they don’t close, discard them.
Heat the oil in a frying pan and sauté the shallots, coriander seeds, lemongrass and lime leaves until softened.
Add the mussels and pour in the beer. Put the lid on and steam for 5 minutes until the mussels have opened. (Discard any that remain closed.) Pick the mussel meat from the shells and return to the broth. Reduce until the volume of the liquid has reduced by half.
Pour in the cream and add most of the chopped chervil. Season with salt and pepper and squeeze over the lime. Keep warm.
Preheat a deep-fat fryer to 180C. (Caution, hot oil can be dangerous. Don’t leave hot oil unattended.)
Dip the cheeks in flour and then the batter. Carefully lower into the oil and deep-fry 5–6 minutes until golden. Drain on kitchen paper.
Serve the deep-fried monkfish cheeks alongside the mussels and garnish with the remaining chervil.