In a food processor, blitz together the lemon and gin. Lay your salmon skin-side down in a roasting tin and pour over the lemon and gin mix. Combine the salt, sugar, thyme and chilli flakes, then spoon over the salmon. Cover with cling film and chill for at least 2 hrs.
Heat oven to 160C/140C fan/gas. Thirty mins before you want to cook the salmon, remove it from the fridge and allow it to come to room temperature. To make the roasting oil, blitz the preserved lemons and olive oil. Gently rinse the cure from the salmon and pat dry with kitchen paper. Lay it skin-side down in an oiled roasting tray and pour over the roasting oil, rubbing it all over the fish. Cover the tin tightly with foil and roast for 15 mins.
Remove the foil and return the fish to the oven for a further 10 mins. Take out of the oven and rest for 5 mins, then scatter over freshly torn dill, to serve.
