Preheat your oven to 350°F (180°C) and lightly grease a 12-hole muffin tin with oil spray.
Melt the butter in a small saucepan over medium heat, then brush a little into each muffin cup and leave the rest in the pan for the sauce.
Add the garlic to the butter and cook for 20 seconds, then stir in the cream, salt, and a few cracks of black pepper, simmering for 30 seconds before taking it off the heat.
Slice the potatoes into 2mm-thick rounds using a mandolin or sharp knife, and try to keep them uniform so they stack nicely and cook evenly.
Layer the sliced potatoes into the muffin cups until they’re about halfway full, matching sizes so each stack looks neat.
Spoon about 1 teaspoon of the warm cream sauce over each stack, then top with a slice of cheese.
Add more potato slices on top until the stacks are just above the rim of the muffin tin, drizzle with the remaining cream sauce, and sprinkle most of the thyme over the tops.
Cover the tray loosely with foil and bake for 40 minutes, or until the potatoes are soft and a small knife slides through with no resistance.
Remove the foil, top each stack with shredded cheese, and bake uncovered for another 10 minutes until bubbly and golden.
Let them cool for 5 minutes so they hold together, then run a butter knife around each one and gently lift them out to serve.