Method

1. Heat the oven to 180 °C and butter a 20x20cm ovenproof casserole dish. 2. To make the sauce, melt the butter in a heavy-based saucepan, stir in the flour and cook for around two minutes. Slowly stir in the milk and cook very gently on a low heat, continuously stirring until the sauce thickens. Add salt and pepper and leave to one side.

3. Melt the butter in a heavy-based pan (I use a large frying pan) and add the leeks, season and allow to sweat for two minutes. Gradually add the spinach to the pan along with the garlic and cook for a further two minutes. When the spinach is wilted and cooked, drain off any excess liquid.

4. Now you are ready to build your lasagne! Start by spooning a layer of béchamel sauce over the bottom of the buttered dish, followed by two sheets of lasagne.

5. Spoon half of the leek and spinach mix over the lasagne, followed by a third of the salmon, then a third of the remaining béchamel sauce and a sprinkling of cheese over the top.