Prepare the potatoes
Peel the potatoes.
Slice very thinly (1–2 mm) using a mandoline (Uniform slices are key for even cooking).
Season the fat
If using taco fat, warm it gently until liquid.
If using butter, mix the melted butter with the spices.
Add potato slices to a large bowl and toss until fully coated.
Layer the potatoes
Line a loaf tin or baking dish with baking paper.
Brush a little butter mixture on the base.
Layer the potatoes tightly in even layers, pressing down frequently to remove air pockets.
Bake
Cover with baking paper and foil.
Bake at 160°C for about 90 minutes until completely tender.
Press and chill
Place another tray on top and add weight (cans or a heavy pan).
Refrigerate at least 6 hours, preferably overnight, until fully compressed.
Portion
Remove the potato block from the tin.
Trim the edges and cut into rectangles or squares.
Crisp the pavé
Pan-fry
Cook in butter or oil over medium heat until deep golden and crispy on all sides.
Deep fry
Alternatively fry at 170°C in neutral oil until golden and crisp.
Drain on paper towel and season lightly with salt.
Serve with chipotle mayo.