Seared Haddock with Mushroom Agrodolce Sauce

Seared Haddock with Mushroom Agrodolce Sauce is nothing short of perfection.  Agrodolce is an Italian sauce which means sweet and sour combined.  The onions cooked down (with button mushrooms) release their amazing sugars and then countered with a top notch Sherry vinegar.  Sear up a beautiful white fish, like haddock, and you’ve got a dish that can’t be beat.  I love doing this in my cast iron skillet so it’s truly stove to oven to table.   Incredible.  Cod works really well in this dish, too.  125% Loon Approved!

Seared Haddock with Mushroom Agrodolce Sauce

Course: Seafood
Cuisine: Italian
Keyword: Haddock
Prep Time: 10 minutes
Cook Time: 20 minutes
Total Time: 30 minutes
Servings: 4
Calories: 216 kcal
Author: Kris Longwell
This Seared Haddock with Mushroom Agrodolce Sauce is divine. The tartness of the sauce compliments the creaminess of the haddock. Don't worry, this isn't a 'fishy' tasting dish at all. Simply amazing, and comes together in about 20 minutes. Perfection!


  • 5 tbsp extra-virgin olive oil
  • 6 cipolline onions peeled
  • 8 oz button white mushrooms, stems trimmed
  • Kosher salt and freshly ground black pepper to taste
  • 1/2 cup good quality sherry vinegar
  • 1 lb haddock cut into 4 individual fillets
  • 6 sprigs of fresh thyme


  1. Heat oven to 400 F.
  2. Bring 2 cups water in a medium pan to a boil over high heat.
  3. Add the onions and cook for 5 minutes. Drain.
  4. Remove skin from onions and cut off root end. Set aside.
  5. Heat 3 tablespoons oil in a medium cast-iron skillet over medium-high heat.
  6. Add onions and mushrooms and a good pinch of salt and pepper and saute, stirring occasionally, until nicely browned, about 7 - 8 minutes.
  7. Add vinegar to skillet and cook for 1 minute, using a wooden spoon to scrape any browned bits stuck to bottom of the skillet.
  8. Transfer onions, mushrooms, and pan juices to a bowl, and set aside.
  9. Wipe the skillet clean with paper towels and return to high heat.
  10. Rub haddock fillets with remaining 2 tablespoons oil, then season generously with salt and pepper.
  11. When skillet is very hot add fillets, skin side up, and sear until a good brown crust develops, about 3 minutes.
  12. Carefully turn cod skin side down, arrange reserved onions, mushrooms, and pan juices around fish, then scatter with fresh thyme.
  13. Place skillet in oven and roast until fish is cooked through, about 12 minutes.
  14. Discard thyme.
  15. Serve on warmed plates and enjoy!


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