Heat oven to 175 degrees F.
Line 2 baking pans with silpats, (French non-stick baking mats) or parchment paper. With very sharp knife, slice grapefruit into 1/16-inch thick slices. Place slices on prepared baking pans.
Place confectioners' sugar in a strainer; sprinkle over grapefruit. Turn chips over, coat with remaining sugar. Bake until chips glisten and have a syrupy coating, 1 1/2 to 2 hours.
Remove baking pans from oven; with tongs, turn chips over.
Return baking pans to oven, rotating shelves. Cook until lightly golden and crispy, 1 1/2 to 2 hours. Transfer chips to rack to cool and harden. Store in an airtight container up to several days.
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