1. Preheat the oven to 180 degC.
2. Cover the dried mushrooms with water and leave for 5 minutes. Drain and squeeze mushrooms to remove excess liquid. Discard grit in the bowl, but reserve the liquid.
3. Melt the butter in a saucepan. When it’s gently foaming, add the thyme and all the mushrooms. After 2 minutes, add the garlic and cook for another 2-3 minutes.
4. Add the tarragon, parsley, season with salt and pepper, and add the lemon juice.
5. Using the same pan to make the sauce, add the butter and onion, and cook for 1 minute. Add flour and continue cooking for about 2 minutes. Add milk, nutmeg, reserved cep liquid and ½ tsp salt. Keep whisking on a low heat until the mixture has thickened. Cook for 10 minutes, then remove from the heat.
6. In a small bowl, mix ricotta (or cottage cheese) and egg, then fold in 3 tbsp of the sauce and the feta. Add the cheddar cheese and parsley (optional) to the remaining sauce in the pot and stir well.
7. Pour boiling water over the lasagne sheets (do this a few at a time to avoid sticking). Soak for 2 minutes. Remove and dry on a paper towel. Into a well-greased 25 x 35cm dish, place one-fifth of the sauce, cover with lasagne sheets and spread 1/4 of the ricotta mix on top, scatter over 1/4 of mushrooms and 1/4 of mozzarella. Repeat and finish with a layer of pasta, covered with sauce.
8. Sprinkle parmesan on top and cover loosely with foil – always avoid foil sitting directly over a lasagne – and bake for 40 minutes or until sauce is bubbling around the sides. Remove foil and bake a further 10 minutes for top colour. Leave to rest for 10-15 minutes for ease of serving.

Cook's tip: You can make this the day ahead – slice it cold and re-heat in the microwave if desired. Don’t worry if when you cut it you do not achieve the perfect slice – always have plenty of grated parmesan on hand to cover any issues. Like icing sugar with desserts, it can hide a multitude of sins!