Salmon with Agrodolce Sauce
3 Tablespoons olive oil, divided
2 medium red onions (about 1 lb. total)
each cut into 8 wedges
2/3 c. balsamic vinegar
1 teaspoon sugar
1 Tablespoon unsalted butter
Heat 1 Tablespoon oil in a 12" nonstick skillet over medium heat until hot. Pat salmon dry and sprinkle with 1 teaspoon salt and 1/2 teaspoon pepper, then cook, skin side up, until bottom side forms a golden crust, 12 - 15 minutes. Turn fish over and cook until just cooked through, about 3 minutes more.
Meanwhile, heat remaining 2 Tablespoons oil in a large skillet over medium high heat until it shimmers, then saute' onions until golden brown and crisp-tender, 6 - 8 minutes. Stir in vinegar, sugar and 1/2 teaspoon salt and cook until sauce is syrupy about 2 minutes. Remove from heat and stir in butter.
Spoon onions with sauce onto plates and top with salmon, skin side down.