Salmon with Agrodolce Sauce
- 4 6-ounce salmon fillets (1 inch thick) with skin
- 2 medium red onions (about 1 pound total)
- 3 tablespoons olive oil
- 1 tablespoon unsalted butter
- 2/3 cup balsamic vinegar
- 1 teaspoon sugar
Heat 1 tablespoon oil in a 12-inch 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 undersides form a golden crust, 12 to 15 minutes. Turn fish over and cook until just cooked through, about 3 min...