Method
1. Preheat your oven to 220°C/Fan 200°C/Gas 7. Brush your mushrooms clean, then thickly slice them. Scoop them into a large bowl. Season generously with salt and pepper. Toss well to coat.
2. Line a large baking tray with foil and spread the mushrooms out on it. Bake in the oven for 15 mins, then take out and give everything a stir. Bake for a further 10 mins or till the mushrooms are tender and have reduced in volume. Take out of the oven and set aside. Turn the oven down to 190°C/Fan 170°C/Gas 5.
3. Meanwhile, peel and finely chop the onions. Warm 2 tbsp olive oil in a large pan over a low heat. Add the onions. Season with salt and pepper. Pop a lid on the pan and gently fry, stirring occasionally, for 10 mins till the onions are soft. Peel and crush the garlic. After 10 mins, add it to the onions. Fry, stirring, for 2 mins or ill the pan smells aromatic.
4. Add the butter. When it has melted, add the flour and cook, stirring constantly for 2 mins to cook the flour. Add a small splash of milk and stir to combine it with the roux. Repeat till you have smoothly incorporated the milk with the roux. Drop in the bay leaves. Bring up to a gentle simmer, then turn the heat down and bubble for 6-8 mins, stirring occasionally, till the sauce has thickened.
5. Meanwhile, pick the parsley, sage and thyme leaves off their sprigs. Finely chop them. Coarsely grate the Emmental. Finely grate the zest from the lemon.
6. When the sauce has thickened, lift out the bay leaves. Pour in the cream. Add the chopped herbs, lemon zest and Emmental cheese. Stir well to melt the cheese. Take off the heat. Add more salt and pepper, if you think the sauce needs it.
7. Arrange 4 sheets of the pasta in an ovenproof dish. Cover with 1/3 of the sauce. Top with half the mushrooms. Drizzle over 2 tbsp pesto. Top with 4 more sheets of lasagne. Add another 1/3 of the sauce and the remaining mushrooms. Drizzle over 2 tbsp pesto. Top with 4 more sheets of lasagne, then spoon over the last of the sauce. Drizzle over the remaining pesto. Tear over the mozzarella. Finely grate over the veggie parmesan.
8. Bake for 35-40 mins or until golden and bubbling. Let the lasagne cool in the dish for 5-10 mins before serving.