Wash and dry the oranges, then slice them into 1/4 inch thick rounds with a sharp knife or mandoline, removing any seeds.

Add the 3 cups granulated sugar and 3 cups water to a wide saucepan and place over medium heat. Stir until the sugar dissolves and the syrup comes to a gentle boil.

Reduce the heat to maintain a gentle simmer. Arrange the orange slices in the pan in a single layer so they are mostly submerged and not tightly overlapping.

Simmer the orange slices for 45 to 60 minutes, turning them every 10 minutes, until the peel and flesh look glossy and translucent and the slices are tender but still hold their shape. Adjust the heat as needed to keep the syrup at a light simmer without vigorous boiling.

Use tongs to lift the candied orange slices from the syrup, letting excess syrup drip back into the pan, and place the slices flat on a wire rack set over a sheet pan.

Let the slices dry uncovered at room temperature for 24 hours, or up to 48 hours, until they feel firm and tacky rather than wet.

For a sugar coated finish, roll each dried slice lightly in additional granulated sugar, shaking off any excess.

For chocolate dipped orange candy, dip one half of each dried slice in melted chocolate, place back on the wire rack or parchment lined tray, and sprinkle with a pinch of flaky sea salt if desired. Allow the chocolate to set completely before serving or storing.