Rinse the yellow turnips and let them drain for a few minutes in a sieve. Cut off the green stems and then peel the turnips. Grate the turnips finely.

Put the soft butter on a large oven tray and rub it all over using your fingers (or a piece of kitchen paper if you like).

Then transfer the grated turnips to the tray. Try to spread the turnips evenly so that they can cook evenly as well. Season them with a little pepper and salt.

Sprinkle the grated turnips with the grated cheese. Then season one last time with a pinch of pepper and salt.

Bake the grated turnips in a preheated oven at 392°F (200°C) for 30 to 35 minutes until the cheese has melted and the sides of the turnip au gratin start to brown. Then turn the oven off but leave the turnips inside for another 20 minutes to rest. Remove the turnip gratin from the oven. Cut it up and serve.