Heat one to two tablespoons of oil in a pan or pot so that the bottom is just covered with it. Add the corn grains and let it pop up in a closed pot. Bring milk and 1/8 litre water to the boil, stir in sauce powder. Season with nutmeg and simmer for one minute. Sort the spinach, wash thoroughly and drain a little.
Peel and chop onion and garlic. Wash, clean and slice the mushrooms. Fry briefly in the remaining oil. Season with salt and pepper and remove from the pan. Sauté onion and garlic in frying fat. Add spinach dripping wet. Let them collapse. Season with salt and pepper. Clean, wash and slice the tomatoes. First layer mushroom slices, then spinach and finally tomato slices in a flat casserole dish.
Let them collapse. Season with salt and pepper. Clean, wash and slice the tomatoes. First layer mushroom slices, then spinach and finally tomato slices in a flat casserole dish. Pour on the sauce. Grate cheese and mix with the popcorn. Sprinkle over the gratin in a preheated oven (electric range: 200 °C/ gas: level 3) and bake for 20 minutes