1 tbsp olive oil
1 large white onion, sliced
2 garlic cloves, chopped
2 bay leaves
1kg/2lb 4oz wild mushrooms, sliced
250ml/9fl oz vegetable stock
1 tbsp tomato purée
sea salt and freshly ground black pepper
375g pack fresh lasagne sheets
300g/10oz Fontina cheese, grated
50g/2oz Parmesan cheese, finely grated
FOR THE BECHAMEL SAUCE
2 tbsp plain flour
¼ tsp freshly grated nutmeg
750ml/1¼pt full-fat milk
Make the béchamel sauce. Put the butter in a saucepan set over medium heat. When the butter sizzles, stir in the flour and nutmeg. Cook for 1 min, stirring constantly. Remove from the heat and pour the milk into the pan, whisking constantly. Return the pan to low heat and cook for 5 mins, stirring constantly, until the sauce is smooth and creamy.
Preheat oven to 180C/fan 160C/gas 4. Put the butter and oil in a frying pan set over high heat and add the onion, garlic and bay leaves. Cook for 5 mins until the onion has softened and turned opaque. Add the mushrooms, reduce the heat to medium and cook for 15 mins, stirring occasionally until the mushrooms are evenly cooked. Add the stock and tomato purée and increase the heat to high. Simmer rapidly until the liquid has reduced by half. Season well with salt and pepper.
Line the bottom of an oiled baking dish with lasagne sheets. Spread over a quarter of the b échamel sauce. Add one-third each of the mushrooms and grated Fontina cheese. Repeat the process and finish with a layer of lasagne. Spoon over the remaining sauce and sprinkle with Parmesan. Bake in the preheated oven for 45 mins, until golden brown and bubbling. Leave to rest for 10 mins before serving.