Preheat your oven to the lowest possible setting, typically around 200°F (95°C). Line two large baking sheets with parchment paper.

Wash the oranges thoroughly under cold running water and dry them completely with a clean towel.

Using a very sharp knife, slice the oranges into uniform rounds, about 1/8 to 1/4 inch (3-6mm) thick. Thinner slices will dry faster and become crispier, while slightly thicker slices will remain a bit more chewy. Discard the end pieces and remove any visible seeds.

Lay the orange slices out on paper towels in a single layer. Gently pat the top of the slices with more paper towels to remove as much excess moisture as possible. This step is crucial for faster and more even drying.

Arrange the patted-dry orange slices on the prepared baking sheets in a single layer, ensuring none of them overlap. Give them a little space for air circulation.

Place the baking sheets in the preheated oven. Bake for approximately 2 to 4 hours. The exact time will depend on the thickness of your slices and your oven's efficiency.

Flip the orange slices every 60 minutes to ensure even drying and prevent them from sticking to the parchment paper. Continue baking until the slices feel dry, slightly leathery, and firm to the touch. They should still have some pliability but not feel moist.

Once they reach the desired dryness, turn off the oven and leave the orange slices inside with the oven door slightly ajar for another 30-60 minutes, or until the oven cools completely. This helps them crisp up further and ensures all moisture is gone.

Remove the dried orange slices from the oven and transfer them to a wire rack to cool completely. They will crisp up even more as they cool.