Preheat oven to 220°C / Fan 200˚C.
Cut four squares of foil and four matching squares of baking parchment, so about 40 cm a side ... but is will be dictated by the rolls of foil and parchment you have
Take one sheet of baking parchment, and place on top of a square of foil, and then fold in half. Repeat for each piece so that you have 4 folded squares.
Unfold each of the pieces of parchment and foil, and place a quarter of the potatoes on one side of each of the squares. Add two cloves of the garlic into each package, with a sprig of the fresh thyme. Season with a little salt and pepper, and place some butter slices on top.
Fold the foil and parchment over the top of the potatoes, then fold over each edge, working your way all around, folding lengths of 4cm. You can overlap the edges and the finished parcel should be a semi-circle shape.
Make sure all edges are firmly pressed down so that no steam can escape – you can use a knife handle to ensure that the parcels are secured.