Prepare the mushroom pate: fry the minced onion on oil for 1 minute together with chopped thyme and black pepper. Add cleaned mushrooms, sliced in bigger pieces, and chopped garlic. Add salt and fry for 5 minutes under occasional stirring. Mix the blend into fine pate. Finally, add chive.
Clean the meat and remove sinews by a sharp knife. Dry it, rub with salt, spices and oil. Place in one piece on the grill or pan and roast each side for 1 to 1.5 minutes. If you wish to have it more cooked, do a test by pressing it and adjust the grilling time according to the juice running out. Using a sharp knife, cut the warm steak into thin strips perpendicular to the fibers.
Prepare gratinated potatoes: cut the cleaned potatoes into fine slices and put them in a greased oven dish. Mix milk, cream and eggs, adding a smack of nutmeg, spice and salt. Pour it on the potatoes, cover and bake in oven heated to 180°C for about 40 minutes.