Preheat your oven to 140°F (or to its lowest temperature) and place a rack in the center of the oven.

Wash and dry all 5 oranges. Using a sharp knife, slice each orange into thin, even rounds.

Line one or more baking sheets with parchment paper. Set wire cooling racks on top of the parchment-lined sheets (or use the parchment-lined sheets alone), so air can circulate around the slices and any drips are caught on the parchment.

Arrange the orange slices in a single layer on the wire racks (or parchment), making sure slices do not overlap.

Place an oven thermometer on the same rack near the slices to monitor the actual temperature.

Put the sheets/racks in the oven and leave the oven door slightly open to allow moisture to escape.

Dry the slices, checking them regularly. Every 30–60 minutes, rotate the baking sheets or swap rack positions and, if needed, flip the slices so they dry evenly. Continue until the slices are dry to the touch and no longer tacky (they may be leathery or crisp, depending on thickness).

Remove the trays and let the orange slices cool completely on the racks to room temperature.

Once fully cooled, store the dried orange slices in an airtight container.