Atun Encebollado: Tuna Seared Under Sweet Onions

Basque

Medium · Hot

Atun Encebollado: Tuna Seared Under Sweet Onions

The onion and bell pepper are cooked long before the tuna appears, collapsing into a golden, yielding bed that smells of olive oil and something almost sweet. A quick sear brings the tuna to the edge of cooked, a splash of white vinegar cuts the richness clean, and then it all rests together in the pan. The onion does the work; the tuna just has to not be overcooked.

Recipe by

Aitor Elizondo

The Pintxo Purist

Prep

10 min

Cook

35 min

Rest

5 min

Total

50 min

Method

Caramelize the Onions

In a heavy-bottomed skillet or cazuela, warm the olive oil over medium-low heat. Add the sliced onions and garlic, season with a pinch of salt, and stir to coat.

Cook slowly, stirring occasionally, for 25–30 minutes until the onions are deeply golden, jammy, and sweet. Reduce heat if they color too fast — this is not a race. Remove from heat and keep warm.

Sear the Tuna

Season the tuna steaks generously with salt and white pepper on both sides. Let them rest at room temperature for 5 minutes.

In a separate cast-iron skillet, heat a tablespoon of olive oil until it shimmers and just begins to smoke. Sear the tuna steaks for 90 seconds per side — you want a dark, caramelized crust on the exterior while the center stays rosy and rare. Do not move them until ready to flip.

Plate and Serve

Spoon a generous mound of the sweet onion mixture onto each warm plate. Lay a seared tuna steak over the onions — the residual heat will gently finish cooking the interior.

Drizzle a thread of good olive oil over the fish, dust with chopped parsley, and serve immediately with crusty bread to soak up every drop of the onion juices.

Nutri-Score

Excellent balance

A–E · lower is better · score -1

Calories

348

per serving

High in protein · 29gLow sugar · 6g

Protein

29g

Carbs

12g

Fat

20g

Sat. fat

Fiber

Sugar

Sodium

1055mg

Gluten FreeDairy FreePescatarianLow CarbMediterraneanWhole30PaleoHeart HealthyAnti InflammatoryDiabetes FriendlyLow Sodium AdaptableThyroid SupportHigh ProteinWeight ManagementMuscle RecoveryBalanced MealOmega3 Rich

Nutri-Score is a general nutritional-balance guide, not medical or dietary advice.

Flavor Profile

Umami

Sweet

Salty

Sour

Bitter

Spicy

Textures

CrispyTenderSilky

Aromas

HerbalSmokyFattyCaramelized

Kitchen Equipment

Primary Tool

Cast Iron Skillet

Frying PanCast Iron PanChef Knife Cutting Board

Counter FootprintMedium

Techniques

CaramelizingPan SearingResting

Safety & Storage

Cooking Temperature

Tuna is intentionally seared to rare (90 seconds per side with rosy center). This does not reach safe internal temperature for high-risk populations.

High Risk Population

Pregnant women, young children, elderly, and immunocompromised individuals should consume fully cooked fish. Consider searing 2-3 minutes per side for these individuals.

Cross Contamination

Use separate cutting boards and utensils for raw tuna. Never place cooked fish on plates or surfaces that touched raw tuna without sanitizing first.

Storage

Refrigerate fresh tuna at 40°F or below. If purchasing day-of, cook immediately. Leftover seared tuna must be consumed within 1-2 days or frozen.

Handling

Bring tuna to room temperature only after patting dry. Excess moisture prevents proper sear and crust formation. Rest at room temperature for maximum 10 minutes before cooking.

Equipment Safety

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Allergen Warning

This dish contains fish. For catering or restaurants, declare fish as an allergen to customers per food safety regulations.

Pro Tips

Technique

Do not touch the tuna during those 90 seconds. I have watched amateurs nudge the steaks like they are checking on a sleeping child — the crust will break and all that beautiful sear is lost. Let the cast iron do its work, then flip with confidence.
If your onions start to color before 20 minutes, your heat is too high. I do not care if you are impatient. Turn it down. The difference between jammy onions and burnt onions is the difference between a sidrería and a sad plate.

Substitution

Fresh tuna can be hard to find outside the coast — if using frozen, thaw slowly in the refrigerator overnight and pat completely dry before searing, or the exterior will steam instead of crust.

From the chef

In the sidrerías of Errenteria, this is what the workers ate after the cider had been poured and the txuleta carved — simple, honest, and better than anything on a menu with white tablecloths. My father would say the onions must weep their sweetness before the tuna speaks, and after thirty years in the kitchen, I still agree. This is Atlantic cooking at its most loyal: the fish stays rare because it earned the right to stay rare, and the onions take their time because patience is the one ingredient nobody can fake.

Aitor ElizondoThe Pintxo Purist

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TagsTunaSearedCaramelized OnionsOlive OilGarlicBasqueSeafoodGluten Free

AllergensFish

Source: generated · May 30, 2026