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A white plate filled with filet of seared haddock topped with mushroom agrodolce sauce.

Seared Haddock with Mushroom Agrodolce

Course: Seafood
Cuisine: Italian
Keyword: agrodolce sauce recipe, easy seafood recipe, How to cook haddock
Prep Time: 10 minutes
Cook Time: 20 minutes
Total Time: 30 minutes
Servings: 4
Calories: 315kcal
This Seared Haddock with Mushroom Agrodolce is divine. The slightly sweet, slightly tart sauce compliments the creaminess of the haddock perfectly. Don't worry, this isn't a 'fishy' tasting dish at all. Simply amazing, and comes together in about 30 minutes. Perfection!
Print Recipe


  • Skillet and baking dish (or cast-iron skillet)


  • 5 tbsp extra-virgin olive oil divided
  • 6 cipollini onions about 1 cup, or boiling or pearl onions
  • 8 oz mushrooms white button, stems trimmed
  • Kosher salt
  • black pepper freshly ground
  • ½ cup balsamic vinegar
  • tbsp sugar
  • 1 lb haddock cut into 4 individual fillets
  • 6 sprigs thyme fresh, plus more for garnish, chopped


  • Heat oven to 400°F.
  • Bring 2 cups of water in a medium pan to a boil over high heat. Add the onions and cook for 1 minute. Drain. When cool enough to handle, use a knife to snip off the ends of the onions. Use your fingers to gently squeeze the onion out of the skin. Set aside.
  • Heat 3 tablespoons of oil in a large saucepan/skillet over medium-high heat. Add onions and mushrooms and a good pinch of salt and pepper and sauté, stirring occasionally, until nicely browned and soft, about 10 to 12 minutes.
  • Add vinegar and sugar to the skillet and simmer. Stir frequently with a wooden spoon to scrape any browned bits stuck to bottom of the skillet. Cook until sauce thickens slightly and comes almost like syrup, just a few minutes. Transfer onions, mushrooms, and sauce to a bowl, and set aside.
  • Rub haddock fillets with remaining 2 tablespoons oil, then with salt and pepper. If the skillet is dry, add another tablespoon of olive oil and heat over medium-high heat.
  • When the skillet is hot, add fillets, skin side up, and sear until lightly browned on the bottom, about 4 minutes. Remove from heat and place the fish, seared side up, in a baking dish. Pour the mushroom agrodolce sauce all over the fish and top with the sprigs of thyme.
  • Place in oven and roast until fish is cooked through, about 10 minutes. Remove from oven and discard the thyme sprigs on top. Plate and garnish with a pinch of chopped fresh thyme. Serve at once.



Pearl onions or boiler onions are perfectly fine substitutions for cippolini.  Frozen pearl onions can be used in a pinch.  Let thaw before adding them to the skillet.
We love leaving the mushrooms whole, but they can be quartered or sliced, if desired.  Any variety of mushroom will work for this dish but we think good ole white button work wonderfully.
Substitutions for haddock are cod, grouper, halibut, or sole.  Any kind of white, flakey fish will do great.  We find haddock in the frozen seafood section at Whole Foods.   Fresh is always best, but the frozen filets from Whole Foods are still delicious. 
The sauce can be made up to 24 hours in advance.  The sauce can also be frozen for up to 1 month.  The finished dish will keep in the refrigerator for a couple of days, although, fresh will always be best.  
This is great served with braised Brussel sprouts or mashed potatoes.  It's also excellent over risotto. 


Calories: 315kcal | Carbohydrates: 16g | Protein: 21g | Fat: 12g | Saturated Fat: 3g | Cholesterol: 61mg | Sodium: 254mg | Potassium: 606mg | Fiber: 1g | Sugar: 12g | Vitamin A: 65IU | Vitamin C: 5mg | Calcium: 31mg | Iron: 1mg