Defrost spinach. Peel onions and garlic, finely dice or chop. Sauté half of them in 1 tablespoon of oil. Add squeezed spinach, season with salt, pepper and nutmeg. Stir in creme fraiche, then set aside. In a tall skillet, fry ground beef in 1 tablespoon hot oil until crumbly.
Add remaining onion mixture, season with salt, pepper and paprika. Add broth and tomatoes and simmer about 10 minutes. Fold in thyme. Cut the mozzarella into slices. Preheat oven to 200 degrees.
Grease a large baking dish and put a layer of lasagna sheets in it. Alternate layers of spinach mixture, lasagna sheets and tomato mince sauce until all ingredients are used up. While doing this, finish with tomato mince sauce. Place mozzarella slices on top. Bake mincemeat casserole in oven at 200 degrees for about 30 minutes.