To make the kefir and sorrel sauce, mix together the mustard and honey in a small bowl. Add the lemon juice and zest and season with salt.
Blend 75g/2½oz of the sorrel with the rapeseed oil and pass through a fine sieve. Add the white wine vinegar and mix well, then add the mustard, honey and lemon mixture and stir to combine. Add the kefir and season to taste with salt.
To make the pickled celeriac, place the celeriac in a bowl and sprinkle over some fine sea salt. Leave to macerate for 30 minutes, then rinse with cold water. Add a squeeze of lemon juice and the capers, mix through and set aside.
To make the rye crumbs, place the bread in a food processor and pulse into rough crumbs. Heat the butter in a frying pan over a medium heat until foaming and add the crumbs. Fry until crisp then stir through the chives and drain on kitchen paper.
To make the scallops, heat the rapeseed oil in a frying pan and fry the scallops for 2-3 minutes, until golden-brown.
To serve, mix the shredded sorrel with the celeriac. Place the scallops in the shells and top with the rye crumbs, sorrel and celeriac mix and drizzle over the sauce.