Pre-heat the oven 200c/180 fan Gas 6. Lightly oil an oven proof casserole.
Jane uses a 30cm x 20cm x 10cm
Heat the oil in a pan and saute the onions, garlic and leek until soft. Set aside.
Saute the spinach until soft, transfer to a colander and set aside to allow any moisture to drain.
To make the sauce, melt the butter in a saucepan, whisk in the flour and stir for 2 minutes. Gradually add the milk, whisking all the time and continue cooking until the sauce has thickened. Crumble in the stock cube and mix well. Add the cheese, chopped parsley and dill. Add black pepper and salt if required.
Cover the base with lasagne sheets, spread with half of the leek mixture and then add half of the salmon . Top with one-third of the white sauce. Repeat for a second layer, then add a final layer of lasagne, the sliced tomatoes, pour over the remaining white sauce and finish with the remaining grated cheese.
Cook for 30-40 minutes or until golden and bubbly.