Peel and slice the potatoes in 2mm or 1/10th of an inch in thickness. You can use a knife or a mandolin to achieve this.
Fit the potatoes vertically in a 22x18cm / 8.5x7in. When the mould is full, place more slices of potato in places where you see empty spaces. It needs to be super tight.
Sprinkle the potatoes with the salt and pepper.
Mix the olive oil and butter in a small bowl. Use a brush to paint it on the potatoes.
Spread the cheese on top of the potatoes.
Bake the potatoes in a preheated oven at 200°C / 390°C for 45min or until it's really crispy on top and soft underneath. To make sure they're cooked through, poke them with a pointed knife.
Finish it off with fresh thyme leaves.