Heat oven to 400 degrees. Line a baking sheet with parchment paper. Using a brush, paint a thin, even coating of butter on the parchment; sprinkle lightly with salt and pepper.
Using a French or Japanese mandoline, slice the potatoes lengthwise into even, translucent slices. Place the slices 1/4-inch apart on the buttered parchment. Brush potato slices with butter, leaving no streaks or puddles. Place 1 or 2 parsley leaves on each slice, and flatten with your fingers. Place a matching-size potato slice on top; flatten with your fingers, brush with butter, and lightly sprinkle with salt and pepper. Cover potatoes with a piece of parchment paper, and place another sheet pan on top. Weight the top pan with three bricks, or completely fill pan with raw beans.
Bake, rotating the baking pans together until potatoes are crisp and golden brown all over, about 12 minutes (check between pans after 6 minutes). Remove chips from oven, and serve.
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