Mix the salt, sugar, fennel seeds and dill together in a bowl. Line a large dish with cling film and cover it with half the salt mix. Put the pollack fillet on top and cover it with the remaining salt mix. Bring the cling film over the top and cover the fish completely. Put the fish in the fridge and leave it to cure for at least 8 hrs or overnight. After this time, the fish will be very firm and have a salty flavour. Wash the salt off, put the fish in a large dish, cover completely in cold water and leave to soak for 30 mins. Drain and dry with kitchen paper.
Heat oven to 150C/130C fan/gas 2. Put the fish in an ovenproof dish or roasting tin. Pour the rapeseed oil over the top of the fish and cover the tin with a sheet of foil, seal it around the edges and cook in the oven for 25 mins. Remove from the oven and leave, covered with the foil, until needed for serving. Can be done several hours ahead and left to sit at room temperature.
Whisk the crème fraîche in a bowl with a pinch of salt and cayenne for 2-3 mins until it thickens like clotted cream. Fold in the chopped dill and lemon zest. Cover with cling film and keep in the fridge until needed.
Wash the radishes and cut in half lengthways. Put the taramasalata and the lemon juice in a bowl and whisk together. Remove the pollack from the oil (see tip, below), drain it on kitchen paper to remove the excess oil, then flake the fish onto a large serving plate. Add 3-4 tbsp of the cooking oil to the taramasalata and whisk together. Add the radishes, chives and the smoked paprika to the dressing and fold it all together, making sure the radishes get a good coating. Serve the warm fish with the dill, cream and the radish salad. Toasted brown bread goes really well with this too.