Trim the green part off the leek then shred the white part very finely; using a mandolin will help. Wash thoroughly and drain. Melt the butter in a large frying pan and add the leeks, cover, then cook gently for about 10 minutes, checking them to make sure they haven’t browned. Take off the lid and keep cooking to evaporate off any liquid. Season well. Stir in half the cream and the parsley.
Heat the oven to 190C/fan 170C/gas 5. Lay 2 sheets of lasagne in the bottom of a small dish that is roughly the same size as the 2 sheets. Add a layer of leek – use about 1/3. Scatter over half of the crab meat followed by 1 tbsp capers. Add another layer of lasagne, another 1/3 of leek, the remaining crab meat and 1 tbsp capers. Finish with another layer of lasagne and the remaining leek and capers. Spoon over the remaining cream and sprinkle with the cheese.