Chop the onion and garlic, add to the olive oil, which is not too hot, and fry until translucent. Add the spinach and let it thaw. Add enough crème fraîche and milk to make a pleasant sauce. Season everything well with salt, pepper and Italian herbs. It can taste a little salty, because that is canceled out by baking with the gnocchi.
Put the gnocchi in the baking dish and sprinkle the parmesan on top. Quarter or halve the cherry tomatoes and add to the spinach sauce. Put everything in the baking dish, mix and then spread the cut mozzarella on top.