First, for the pickles, cut the cucumber into rounds and layer it in a sieve, sprinkling with 2 tsp salt as you go. Set over a bowl and leave for a couple of hours – the salt will draw out the moisture.
Bring 200ml water to the boil in a pan with the white wine vinegar, sugar, 1 tsp salt, celery seeds and black peppercorns. Leave to cool.
Peel the carrots and cut them into batons. Clean the radishes really well, then cut them in half lengthways. Squeeze the drained cucumbers of excess moisture.
Put all the vegetables in a 1-litre sterilised jar with the dill and pour the cooled vinegar over them, then seal with a lid. Leave to sit at room temperature for two days before serving, or keep chilled. Will keep in the fridge for four weeks.
Heat the oven to 190C/170C fan/gas 5 and put the salmon fillets on a baking sheet. Brush the fillets with the melted butter and scatter with black pepper. Cook for 14 mins.
Serve the salmon with some of the pickled vegetables, a generous tablespoon of crème fraîche on each fillet, finished with a spoonful of salmon roe on top.