Pour the cream and milk into a saucepan then add the rest of the rosemary and garlic, half the Parmesan and a little seasoning. Gently heat for 3 minutes.
Pour the cream mixture over the layered vegetables. Sprinkle over the remaining Parmesan, cover the whole dish with foil and
If you don’t like Parmesan, just replace it with a good quality cheddar, or if you want the gratin to be extra cheesy, sprinkle cheddar on top in addition to the Parmesan.