Peel the apples and slice as thinly as possible using a slicer or mandoline. Reserve in a bowl or hotel pan covered with plastic wrap to delay oxidation.
Bring the syrup to a boil and pour over the apple slices. Make sure the apples are submerged in the syrup. Reserve the apples in the syrup under refrigeration until needed.
Preheat an oven to 75°C / 170°F.
Line a sheet pan with a nonstick rubber mat and place the apple slices on it in a single layer. Pat them dry with a paper towel.
Bake until the apple slices are firm, about 2 hours. Take them off the nonstick rubber mat while they are hot and let them cool on a marble surface. If they cool off on the rubber mat, it will be nearly impossible to take them off without breaking them.
Reserve in an airtight container at room temperature with silica gel packs. Discard once they begin to soften (they won’t soften unless they are exposed to moisture, so their shelf life is directly related to this).