For the Greek pancake, whisk together flour, milk, salt, eggs, mineral water and nutmeg.
Wash spinach and dry in a salad spinner. Peel and dice the onions and first sauté the onion in a little melted butter, then add the spinach and cover. Let cook for 10 minutes, then season with salt and pepper. Collect spinach in a sieve and squeeze a little.
Grate the Gouda. Fry pancakes from the dough in batches in melted butter on both sides and place one in a greased round baking dish. Place some spinach on top, then spread a portion of strained tomatoes on top, sprinkle with Gouda and repeat the process until all ingredients are used. Finish with spinach.
Preheat oven to 250 °C.
Roast pine nuts in a pan without fat, crumble feta and sprinkle both over the dish. Bake the Greek pancake on the lowest rack for 20 minutes.