Peel and wash the potatoes and cook for about 20 minutes in simmering salted water until fork tender completely through to the centre.
While the potatoes boil, chop the garlic and sauté it for a few minutes in the butter in a small saucepan; just until the garlic softens a little but not browned.
Mash the potatoes so that there are no lumps then mix in the scalded cram and garlic butter along with the grated cheese and a pinch of pepper to season; plus the thyme if you are using it.
Using the back of a fork, draw ridges all across the surface of the potato in both directions, just to create a bit of a craggy surface.
Note: I don't use additional salt with the pepper to season these potatoes before baking. Bothe the butter and the parmesan cheese contain adequate salt to season the potatoes well.