Heat the butter over a medium heat in a saucepan. When the butter is foaming, add the potatoes(peeled, cut into barrel-shapes using a cookie cutter) and fry until deep golden-brown on one side, about 1 minute. (Do not move the potatoes as they cook.) Turn over the potatoes and cook for a further 1 minute, or until golden-brown on both sides. Carefully pour in the stock, then add the garlic cloves and thyme sprigs. Season, to taste, with salt and freshly ground black pepper. Cover the pan with a lid and place it into the combi oven using hot air, 150°C, 15 minutes, then remove the potatoes from the pan using a slotted spoon and keep warm.