Mix the salt with the cold water and brine the whole duck for 8 hours.
After you have brined and thoroughly rinsed off the duck under cold water, allow it to sit in the fridge with ample airflow to all sides for several hours. A dry duck will make for crispier skin when roasting.
Hours ahead of roasting, cut the shape of the duck breast out of two navel oranges and freeze the breast-shaped pieces. Trim the rind off the cut-out pieces, too, and freeze those as well. You may wish to do this with two sets of two oranges; I’ll explain why shortly.
When you are ready to roast, pre-heat your oven to 275 degrees. Cut your root vegetables or celery and create planks in your skillet.
Set the duck breast-side-up on the planks, allowing for ample airflow on all sides. Stuff the duck’s cavity with the frozen orange slices. Then, place whole frozen oranges (with breast-shaped cuts removed) on top of breasts. You may need to secure the oranges with toothpicks to prevent them from sliding off.
The frozen fruit will slow down the rate at which the breasts cook while also adding that orange flavor that pairs so well with duck. The orange slices inside its cavity do the same thing. (Think of how a stuffed Thanksgiving turkey cooks slower—the flow of heat is restricted and, therefore, the breasts cook more slowly).
Roast the gadwall for at least 50 minutes. You may wish to swap out the frozen oranges at this point (this is where the second pair of frozen oranges comes in handy) and roast for another 30. Be careful not to burn the wings or legs.
Once the sides of the duck are dark golden brown, remove the oranges and allow the duck to roast for 5 more minutes. Turn on broiler and broil for another 5 to crisp up the duck’s skin.
The goal is to cook the duck breasts to about 140 F. Wings and legs should get closer to 190 F. It still may be necessary to throw the wings and legs back into the oven to tenderize. You can also make a glaze from the fat and orange drippings by adding a bit of honey to the skillet and mixing all the juices together.
