Spray a baking dish with cooking spray (or grease with butter).
Thinly slice the peeled potatoes and fennel.
Layer some potato, slightly overlapping to fill the base of the baking dish. Scatter with half the fennel, a generous amount of salt and pepper and a third of the cream.
Repeat another layer of potato, fennel, seasoning and cream then top with a final layer of potato and the last of the cream. Sprinkle over with a generous amount of freshly grated parmesan.
Bake at 180°C covered for one hour, then uncovered for 20 minutes until golden.