In a small saucepan, combine sugar and water. Bring to a boil, and when sugar is dissolved, remove from heat and allow to cool.
Preheat oven to 225 degrees Fahrenheit.
Slice whole apples with a knife or mandolin into 1/8-1/4 inch thick slices.
Dip each apple slice into the cooled sugar syrup coating both sides and shaking off the excess, and place onto a parchment-lined sheet pan. Slices should not overlap.
Bake for 2 ½ hours. Every 30 minutes flip the apple slices so they dry thoroughly.
As they cool, the apple slices will crisp up even more. Store in an air-tight container at room temperature for up to 2 days.