Peel and dice the onion and garlic. Heat 1 tablespoon of oil, sauté the onion and garlic in it. Unthawed spinach and add 8 tablespoons of water. Cover and cook for 10-15 minutes.
Heat 1 tablespoon of oil in a pan. Pat the fillet dry, cut into 8 slices and fry for about 2 minutes on each side. Season with salt and pepper. Remove.
Debark the cheese. Cut the bread into 8 oblique slices and place on a baking sheet. Stir the creme fraiche into the spinach. Season to taste with salt, pepper and nutmeg. Top bread with spinach, fillet and cheese. Bake under the hot grill for 2-3 minutes or in the preheated oven at the highest level for about 5 minutes.