Heat the oven to 180°C. To make the béchamel sauce, melt the butter in a heavy-based saucepan, stir in the flour and cook for 1–2 minutes.

Slowly stir in the milk and cook at a gentle simmer, stirring frequently, until the sauce thickens. Season with salt and pepper to taste. Set aside.

For the lasagne, melt half the butter in a heavy-based pan over a medium-low heat. Add the leek strips, season with salt and pepper and sweat gently for 2–3 minutes.

Add the spinach leaves, a handful at a time, along with the garlic and cook for another minute or two. Drain off the excess liquid.

Use the rest of the butter to grease a large square or rectangular ovenproof dish. Cut the smoked salmon into small pieces, roughly 2 cm square.

Spoon a layer of the béchamel sauce over the bottom of the dish and layer a third of the lasagne sheets on top.

Spoon half of the leek and spinach mixture over the lasagne, followed by a good third of the smoked salmon, then cover with a third of the remaining béchamel and sprinkle some cheese over the surface.

Repeat the layers of lasagne, leek and spinach, smoked salmon, béchamel and cheese, then cover with a top layer of lasagne.

Spoon the rest of the béchamel sauce on top and scatter over the remaining smoked salmon and grated cheese.

Bake for about 45 minutes until the top is a deep golden colour. To check that the lasagne is cooked, insert a knife in the middle; it should meet with minimal resistance.

Scatter the chopped dill on top of the lasagne and serve, with a crisp green salad on the side.