Put the pasta in boiling salted water and cook for about 10 minutes. Peel and finely chop the onion. Clean and wash the spinach. Heat oil in a pot and fry onion until transparent. Add the spinach and let it collapse.
Season with salt and pepper. Cut the feta cheese into small pieces. Wash and clean the tomatoes and cut off a lid. Cut the tomato lid into small pieces. Hollow out the tomatoes. Drain the pasta and let it drain.
Mix with spinach, feta cheese and tomato cubes and fill into the tomatoes. Place the tomatoes in a greased casserole dish and cook in a preheated oven (electric range: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 15 minutes.
Bring the stock and milk to the boil in a saucepan. Bind with sauce thickener. Stir in crème légère. Season to taste with salt and pepper. Wash parsley, chop finely and add to the sauce. Pour the sauce over the tomatoes and serve.