Instructions:

1. Using the ingredients listed above, prepare the béchamel sauce.
   
2. While the sauce is cooking, wash, dry, and finely chop the parsley. When the béchamel is ready, stir in the parsley until well combined.
   
3. Peel and rinse the potatoes, then slice them thinly.
   
4. Clean and slice the mushrooms, setting aside a few slices for garnish.
   
5. Preheat the oven to 180°C/350°F (160°C/320°F for a convection oven).
   
6. Grease a baking dish with butter and sprinkle with breadcrumbs.
   
7. Layer the bottom of the dish with potatoes, seasoning lightly with salt, and spread a few tablespoons of béchamel over them.
   
8. Add a layer of mushrooms, season with a bit of salt, and spread béchamel over them as well.
   
9. Continue layering potatoes, mushrooms, and béchamel until all ingredients are used up.
   
10. Top with the reserved mushroom slices and a sprinkle of ground black pepper.
    
11. Bake in the preheated oven for about 1 hour (45–50 minutes if using convection). Ten minutes before it’s done, sprinkle the casserole with grated cheese and continue baking until golden.