Mary Berry’s Red Pepper, Mushroom & Leek Lasagne

Preheat the oven to 220°C/200°C fan/Gas 7. You will need a 3-litre (5-pint), ovenproof dish.

To make the tomato and vegetable sauce, heat the oil in a frying pan. Add the leeks and fry for 3 minutes, then add the peppers and fry for 5 minutes until the vegetables are soft. Add the garlic and season with salt and pepper.

Measure the flour into a bowl. Mix with half a tin of chopped tomatoes and stir until smooth. Add the remaining tomatoes to the vegetables in the pan, followed by the purée and sugar and then the flour mixture.

Bring to the boil, stirring until thickened, then add the mushrooms and boil for a couple of minutes, stirring. Add the basil and vinegar and check the seasoning.

To make the cheese sauce, melt the butter in a saucepan, add the flour and whisk over the heat for a minute. Gradually blend in the milk and whisk until bubbling and smooth. Add the mustard, three-quarters of the cheese and season with salt and pepper.

Spoon a third of the vegetable sauce into the base of the dish. Spoon over a third of the cheese sauce and sprinkle with a third of the remaining cheese. Lay three sheets of lasagne on top (break the lasagne so they fit neatly without overlapping). Continue with the remaining layers to give 2 layers of pasta and three layers of sauce and finish with the remaining cheese on top.

Bake in the preheated oven for 40 minutes until bubbling and golden brown.

The lasagne can be made completely up to 24 hours ahead.

If using an Aga, bake on the second set of runners in the roasting oven for 35 minutes.

Please note: if you would like this recipe to be vegetarian, use a rennet-free Cheddar substitute.