Lasagna rolls with ham and mushrooms

Lasagne rolled with ham and mushrooms
Remove the stems from the mushrooms, wipe them and slice them finely. Cook them in a sauté pan with a knob of butter, salt and pepper, until they no longer release water, set aside.
Prepare the béchamel by melting the butter in a saucepan, add the flour, whisk for 20 seconds then add the 40 cl of milk little by little. Whisk until it thickens between each addition of milk. Take 100 g that you reserve, salt and pepper the rest and add the Parmesan then the mushrooms and 1 tbsp of parsley sprigs, mix.
Cut the lasagna in 2, cover with a tablespoon of mushroom béchamel, spread well then place the slice of ham and another 1 spoon of béchamel, roll up and place in the dish.