Salmon With Agrodolce Sauce - cooking recipe

Ingredients

3 tablespoons olive oil, divided
4 salmon fillets, 6 oz each
2 medium red onions, each cut into 8 wedges
2/3 cup balsamic vinegar
1 teaspoon sugar
1 tablespoon unsalted butter
1 1/2 teaspoons salt, divided
1/2 teaspoon pepper

Preparation

Heat 1 tablespoon oil in a 12-inch nonsitick 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, 12-15 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.