Preheat the oven to 200 degrees Celsius (392 degrees Fahrenheit) (fan).
Scrub or wash the potatoes. If they are not new, peel them.
Prepare the marinade:Put the oil and lemon juice in a bowl. Add salt and freshly ground pepper. Remove the thyme leaves from the stems. You can do this by picking or cutting them off or by pushing them through a small grater in reverse. Grate the Parmesan and mix it with the marinade. It is now ready for use.
Put the potatoes into the bowl and mix them well so that the marinade is well distributed.
Place the potatoes in an ovenproof dish and make sure to get all the marinade.