2tbsp olive oil 1 large onion, finely chopped 500g (1lb) mushroom, sliced 2 large garlic clove, crushed 30g (10z) plain flour 2 × 400g (140z) cans chopped tomatoes 1tbsp chopped fresh basil 1tsp caster sugar salt and black pepper 500g (1lb) frozen whole leaf spinach, thawed and drained white sauce, made with 90g (30z) each butter and plain flour, 900ml (1½ pints) milk, and 1tsp Dijon mustard 300g (10oz) mature cheddar cheese, grated 150g (50z) no-precook lasagna sheets
1- Heat the oil in a saucepan, add the onion, mushrooms and garlic and cook for 10 minutes or until soft. Sprinkle in the flour and cook, stirring, for 1 minute.
2- Add the tomatoes, basil, and sugar, and season with salt and pepper. Cover and simmer for 20 minutes.
3- Make the white sauce: melt butter in a small saucean. Sprinkle in the flour, and cook, stirring, for 1 minute. Remove form the heat and gradually blend in the milk. Bring to a boil, stirring, until the mixture thickens. Simmer for 2-3 minutes. Add the Dijon mustard.
4- Season the spinach with salt and pepper. Taking 1 teaspoonful at a time, shape it loosely into 24 balls.
5- spoon one-third of the mushroom mixture into a large ovenproof dish, and place 8 of the spinach balls on top. Cover with one-third of the white sauce and one-third of the cheese. Arrange half of the lasagna on top. Repeat layers, finishing with cheese.
6- Bake in a preheated oven at 190 C (375 f, Gas 5) for 35 minutes or until the pasta is tender. Serve hot.