Dab the meat dry and season with salt and pepper. Heat oil in a pan. Fry the meat for 6-8 minutes at medium heat, turning it over.
Wash the spinach and drain well. Peel and finely dice the shallot and garlic. Heat butter in a pot. Sauté garlic and shallot for 2-3 minutes, then add spinach. Steam spinach for about 3 minutes, season with salt, pepper and nutmeg. Drain the spinach in a sieve
Remove the meat from the pan, wrap in aluminium foil and let it rest for about 10 minutes. Wash the parsley, shake dry and chop the leaves finely. Mix mayonnaise, mustard, chopped parsley, 1/4 of Roquefort and yoghurt, season with salt and pepper
Quarter the bread. Cut each piece 3/4 horizontally. Cut the meat into thin slices. Spread a thin layer of Roquefort sauce on the underside of the bread. Add meat and spinach and pour 1 tablespoon of sauce over each. Crumble the remaining cheese on top and serve. Add the rest of the sauce