Pat the duck dry on both sides. Sprinkle both sides with salt.Place in a cold, dry pan skin-side down and turn the heat to medium-low. Cook about 10 minutes, or until the skin is brown and crispy.
Flip the duck, and cook about 6-8 more minutes, or until the duck reaches desired doneness. For medium doneness, cook to 145°F; for medium-well doneness, cook to 155°F; or for well-done cook to 165°. (See recipe notes)After removing the cooked duck from the pan, place it on a cutting board to rest skin-side up.
Leave the duck fat in the pan after removing duck breasts. (You should have ~ ⅛ cup of fat in the pan, slightly more or less is fine.)Whisk together the sauce ingredients and then add them to the pan. Cook over medium heat, whisking constantly, until the sauce is smooth and thickened (about 2 minutes).