Wash skins of potatoes then pierce each one with a fork two or three times.
Place potatoes in a preheated oven at 450 and allow to cook for 45 mins.
Remove potatoes from oven once cooked and allow to cool.
Create a pouch with foil large enough to hold garlic and line with parchment paper then place garlic in pouch and drizzle with olive oil, then seal.
Place garlic in oven at 350 for 40 mins.
Once the garlic is cooked through remove from oven but keep the oven warm on the lowest temperature.
The potatoes should be cool enough to handle so remove the flesh from each potato by dragging away at one side of each potato and, with a fork, pulling out the flesh into a bowl, and place the skins into another bowl.
If you have a potato ricer you can simply place each potato into the ricer and squeeze. The whites of the potatoes will fall through the ricer and the skin will stay in the chamber.
Once you have removed the flesh from all of the potatoes, place potato flesh into an ovenproof bowl, cover with foil and place in the oven to keep warm.
Slice up half the quantity of potato skins into strips as best you can. You will only need half of the potato skins, you can discard the rest or save for another time.
Heat oil in skillet until very hot but not smoking, then carefully add potato strips and thyme and allow to cook until crispy.
Once done, remove potato skins from oil and transfer to a bowl or plate lined with paper towels.
Remove the potato flesh from the oven and transfer to a bowl.
Add garlic, parmesan and 4 tbsp of melted butter and sprinkle salt on top.
Mash vigorously until garlic and parmesan disappears and the butter has been absorbed.
Add another 4 tbsp of melted butter and mash vigorously once more until butter has been absorbed and the potatoes are free of lumps.
Transfer mashed potatoes to a serving dish and top with the potato skins and serve immediately.