2Heat olive oil in a pan over medium heat. Sauté shallot and garlic until soft and translucent. Add mushrooms and cook until golden brown.
3Remove mushrooms from pan, chop finely, and mix with a dash of balsamic vinegar. Set aside.
4Make béchamel sauce: Melt butter in a pan over medium heat, add flour, and whisk to form a roux. Cook for 1-2 minutes. Gradually add milk, whisking constantly to avoid lumps. Season with fresh nutmeg and pepper. Simmer until slightly thickened.
5Remove béchamel from heat and mix with chopped mushrooms and a large spoonful of ricotta.
6In a baking dish, start with a thin layer of the sauce. Layer lasagne sheets (3 or 4). Spread a layer of sauce, sprinkle with Parmesan cheese. Repeat layers. Finish with a layer of sauce, remaining ricotta in small dollops, extra thyme and the rest of the Parmesan cheese.
7Loosely cover the baking dish with aluminum foil and bake for 25-30 minutes. Remove foil and bake for another 10-15 minutes or until golden brown and bubbly. Let cool for 10-15 minutes before serving.