Rinse the spinach well and blanch briefly in a saucepan of salted water. Drain and cool, drain well and squeeze a little bit.
Heat 1 tbsp butter, sprinkle in flour and sweat. Pour in clear soup and milk and simmer gently for about 5 minutes. Season with salt, pepper and a pinch of nutmeg.
Keep 1 ladle of béchamel sauce and mix the rest with the spinach. Season to taste. Then pour the spinach into a buttered baking dish and form 4 cavities. Place 1 raw egg in each hollow. Carefully spread the remaining béchamel sauce evenly around it, sprinkle with Gruyère.
Bake in oven heated to 180 °C for about 10 min, maybe grill briefly.
Serve with cooked, peeled potatoes or baguette.
If you like, you can also put 1 layer of thinly sliced, lightly salted cooked potatoes in the dish as the bottom layer.
Tip: Did you know that one bowl of spinach already covers the entire daily requirement of vitamin K and beta-carotene?