01 - Preheat oven to 275°F. Line a 9x5 inch loaf pan with baking parchment, leaving an overhang on the sides.
02 - Using a mandoline slicer or sharp knife, cut potatoes into 1⁄8 inch thick slices and place them in a large bowl.
03 - Pour melted butter and olive oil over potato slices. Add salt, pepper, and, if using, thyme leaves and minced garlic. Thoroughly toss to coat each slice.
04 - Arrange the potato slices evenly in the prepared loaf pan, pressing firmly after every few layers to eliminate air gaps and ensure compact stacking.
05 - Cover the loaf pan tightly with foil. Place a second loaf pan or heavy ovenproof object on top to compress the potato layers.
06 - Bake for 3 hours until the potatoes are completely tender.
07 - Remove from the oven and cool to room temperature. Refrigerate with the weight on top for at least 12 hours or overnight to set.
08 - Once firm, lift the potato loaf out of the pan using the parchment overhang. Trim edges if desired and cut into thick slices or rectangles.
09 - Heat a generous layer of neutral oil or clarified butter in a nonstick skillet over medium-high heat. Fry the sliced potatoes for 2–3 minutes per side, or until all surfaces are golden and crisp. Drain on paper towels.
10 - Serve hot, garnished with additional salt or fresh herbs if desired.