Preheat oven to 220°C Brush a round 18cm (base measurement) cake pan with melted butter to lightly grease. Place the potato slices in a large bowl. Add the melted butter and gently toss until potato slices are well coated. Arrange one-third of the potato slices over the base of the prepared pan.
Combine parmesan and thyme in a bowl. Sprinkle potato slices with one-third of the parmesan mixture. Season with salt and pepper. Continue layering with the remaining potato slices, parmesan mixture and salt and pepper, finishing with a layer of parmesan mixture.
Bake in preheated oven, pressing the potato down with the back of a large spoon a couple of times during cooking, for 1 hour or until tender and golden. Remove from oven and set aside for 5 minutes to cool slightly. Turn onto a serving plate. Cut into wedges and serve with mixed salad leaves.