Pre-heat the oven to 300F/150C/Gas Mark 2.
Rub the inside edges and the bottom of a thick roasting tray, (approx 32cm by 32cm square, by 6cm high), with the garlic cloves.
Gently melt the goose fat in a small saucepan.
Slice the potatoes into 2mm thick rounds, (using a mandolin will make this considerably easier). Do not rinse the potatoes, as you want to keep as much starch on the potatoes as possible.
Dip each slice of potato into the melted fat and neatly layer the potatoes, overlapping, covering the bottom of the tray.
Repeat this process until you have at least 8 layers of potatoes and you have used all the goose fat. Season lightly with a few thyme leaves and salt and pepper between each layer.
Cut a piece of parchment paper large enough to cover the tray with 2cm overhang on each side. Brush one side with goose fat and press fat side down on top of the potatoes.
Place the tray into the oven and cook for 2 hours. After two hours check that the potatoes are cooked by inserting the tip of a knife through the potatoes, which should be completely soft.
Remove the potatoes from the oven. Cut a thick piece of cardboard 32cm by 32cm, cover with tin foil, and then wrap in cling film. Place the cardboard on top of the potatoes. Place a light weight (a tin of soup would do) on top of the cardboard and leave the potatoes to cool completely, preferably in the fridge overnight.
The next day, remove the cardboard lid, and place the tray onto a hot stove just enough to release the potatoes from the bottom of the tray. Run a knife around the edges and tip the potatoes onto a clean chopping board.
Trim the edges from the potatoes and cut into 6 nice portions.
Place a non-stick frying pan over a medium heat and lay the potatoes into the pan. Cook gently until the undersides are perfectly golden brown, turn the over and place into a pre-heated oven at 350C/180F/Gas Mark 6 until the other side is golden brown and the centre of each portion is hot.
This makes a great accompaniment to most roast meats.
Preparation: 24 mins
Cooking: 15 mins
1/2 bag Rooster potatoes
1 cut garlic clove
150g goose fat
1 tsp fresh thyme leaves
To taste Salt and freshly ground pepper