Preheat oven to 275°F. Line 2 large baking sheets with parchment paper.Using a sharp knife or mandoline, slice apples into 1/8-inch-thick rounds, cutting widthwise through the core. Arrange slices close together in a single layer but not overlapping. Bake for 2 hours, until apples are dry and crisp.Enjoy warm, or carefully remove slices from sheets and transfer to a wire rack to cool. Store at room temperature for 3 to 4 days.