For the crepes, mix together flour, milk, eggs and one pinch of salts until dough is smooth. Set aside
Heat the tomato sauce in a saucepan.
Slice the onion and garlic finely. Cut the spinach. Heat 3 tbsp of olive oil in a pan, cook the onion and garlic for 2 minutes on medium heat before adding the spinach. Once the spinach is cooked, place in a bowl and stir in the ricotta and 25g of Parmesan. Add some salt and pepper then combine well.
Heat some of the olive oil in a pan. Make about 6 crepes and use olive oil every time you make a new one. Set on a plate
Spread some of the ricotta mixture on each crepes and then roll. Spread half of the tomato sauce in an oven-proof dish. Place the 6 crepes on top then pour the rest of the tomato and sprinkle with parmesan. Cut the mozzarella into slices or dices. Spread out on top of the crepes/crespellen.
Bake on 350F for about 30 minutes then gratin ate for 5 minutes at the end.