- Whisk vinegar, honey and orange juice together in a small bowl, then add rosemary.
- Heat oil in large nonstick skillet over medium-high heat till smoking.
- Season salmon with salt and pepper and cook skin side up without moving till well browned about 4-5 minutes.
- Flip salmon skin side down and cook till all but the very center of it is opaque approx 2-3 minutes.
- Transfer to platter and tent with foil.
- Wipe out pan with paper towels and lower heat to medium.
- Carefully pour balsamic mixture into pan..it will splatter.
- Simmer until thick and syrupy, about 5 minutes.
- Remove rosemary sprig.
- Whisk in butter, season with salt and pepper and pour over salmon.
- Serve.