Preheat oven to 200°C for 20-30 minutes.
Prepare your Puffball mushrooms by cutting them into thin slices (no more than half an inch thick) and caramelizing them. You can sear or sauté them in a pan. I usually oil a baking dish and put them in the oven for 20 minutes, turning them every 5 minutes. Make sure that the sheets of mushroom do not stick to the bottom and burn.
Heat a quarter portion of the butter in a pan and fry the chopped garlic on low heat for a few minutes. Add the toasted mushroom sheets and continue to cook for another 5 minutes and then set aside to cool.
Prepare your seasoning by combining all the herbs and spices in a bowl.
Generously rub the seasoning over your mushroom sheets and set aside.
Peel and thinly slice the potatoes vertically (do not wash them as the starch is needed to hold the cake together).
Season the potato slices with the remaining mixture.
Grease a 20cm diameter ovenproof dish and place a layer of potatoes on its bottom.
Layer the potatoes, mushroom sheets, and butter knobs alternatively, finishing with a potato layer on top.
Cover with foil and bake for about an hour or until a knife slides easily into the cake.
Remove from the oven, run a knife around the outside to make sure it's not sticking together, and let it rest for 10 minutes.
Carefully remove onto a baking sheet and serve warm.