Step 1

Heat 2 tbsp of olive oil in a large non-stick frying pan. Gently fry the onions with a generous pinch of salt for 25 minutes or until really soft and starting to colour. Add a knob of butter and the balsamic vinegar, stir for a minute then scoop out into a large bowl.

Step 2

Wipe the pan then add another tbsp of oil and the mushrooms. Cook on a high heat, stirring until they’ve released all their liquid, softened and the liquid has evaporated. Stir in the garlic and cook for a minute. Add the spinach and cook until wilted. Tip the mushrooms and spinach into the onions and mix. Heat the oven to 190C/fan 170C/gas 5.

Step 3

Beat the ricotta with the lemon juice and zest, vegetable stock and lots of seasoning.

Step 4

Pour just-boiled water into a baking dish, ready to soften the lasagne sheets. Put a thin layer of the mushroom and spinach mixture in a buttered baking dish. Top with enough lasagne sheets to cover (briefly dip each sheet into the hot water before layering – this will keep the lasagne juicy).

Step 5

Spread over a third of the ricotta then half of the remaining mushroom and spinach mixture. Cover again with lasagne sheets. Repeat with another third of ricotta and the remaining mushroom and spinach mix. Add a final layer of lasagne sheets and the last of the ricotta. Sprinkle over the parmesan then bake for 35-40 minutes or until golden. Serve with a green salad, if you like.