1. Slice the potatoes and chop the onion.
(Adjust the thickness of the potatoes according to your preference)
2. Melt the butter in a saucepan and stir in the flour.(Low heat)
3. Pour in the milk in portions and add the whipped cream and mix evenly.
4. Add salt and pepper and stir in the grated Parmesan cheese.
5. Stir in the garlic and onion, then stir in the dill.
6. Spread some of the cream sauce in the gratin dish, then add the potatoes and repeat the layers.
7. Cover the top with aluminum foil and cook in a 180 degree oven for about 50 minutes.
8. Remove the foil, add the mozzarella and bake in a 190 degree oven for about 12 minutes until golden brown.
9. Garnish the top with grana padano cheese and dill (can be omitted).