Preheat oven to 180c.
Grease and line a loaf pan (22 x 12 x 6cm/8½" x 4½" x 2½") with baking/parchment paper (leaving a 13cm/5" parchment paper overhang on all sides) and set aside.
In a large bowl, whisk together cream, garlic powder, parmesan cheese, and salt.
150 ml thickened cream, ½ teaspoon garlic powder, 1 tablespoon finely grated parmesan cheese, 1½ teaspoon salt
Peel and thinly slice the potatoes (I use a mandolin for this) placing the slices into the cream mixture as you go, making sure they are all submerged.
1.4 kg potatoes
Place two layers of potato slices into the bottom of the pan.
Starting with this second layer, drizzle a little melted butter in between each layer as you continue with the remaining potato.
30 g unsalted butter
Once you have used all the potato slices, fold sides of parchment paper over the top of the potato, then cover with foil and bake for 1½ hours or until the potato is tender and there is no resistance when it's pierced with the tip of a sharp knife.
Once potato is cooked, allow it to cool slightly for 15 minutes then place another loaf tin of the same size on top and fill this second pan with something heavy (see my notes) then place it in the refrigerator overnight to compress.