Cod with caramelized onions is one of those simple dishes that taste like home: a bed of onions poached until sweet and mellow, cod loins on top, and the oven to bring it all together. The onion releases its juices and sweetens the whole dish, while the cod remains juicy and full of flavor. Humble, comforting cooking that you'll want to have again and again.
Cod with caramelized onions is a dish that thrives on contrast: the deep sweetness of an onion slowly cooked until caramelized against the saline touch and firmness of the cod. It's an ancient combination that works in all kitchens of the Mediterranean, from Portugal to Greece, and which in Spain has a character all its own. The key is to take your time with the onion: the slower the cooking, the sweeter and silkier it becomes.
Ingredients
- 4 desalted cod loins (we use Extra Desalted Clean Cod Loin - 900g)
- 4 large onions (preferably sweet, like Fuentes de Ebro onions)
- 100 ml dry white wine
- 1 tablespoon brown sugar (optional, to speed up caramelization)
- Extra virgin olive oil
- 1 bay leaf
- Fresh thyme
- Salt and black pepper
Step-by-step preparation
- Cut the onions into thick julienne strips, all of the same size. You need a lot of onion because it reduces enormously during cooking: four large onions turn into barely a handful of caramelized onion.
- Caramelize the onion: 25-30 minutes over low heat. In a large frying pan, heat 4 tablespoons of oil over low heat. Add all the onion at once with the bay leaf, a pinch of salt, and, if you wish, the brown sugar. Cook, stirring every 4-5 minutes, without rushing, without increasing the heat. The onion should first become transparent, then soft, and finally dark golden with a jam-like texture. If it starts to stick, add a splash of water. Don't leave it unattended: there is a fine line between caramelized and burnt.
- When the onion is dark and sweet, add the white wine and increase the heat for a moment to evaporate the alcohol. Cook for 2 more minutes, stirring. Remove the bay leaf.
- Preheat oven to 200°C. Spread the caramelized onion in an oven-safe dish, forming an even bed. Place the cod loins on top, skin side up. Add a few sprigs of thyme, drizzle with oil and black pepper.
- Oven: 12-15 minutes at 200°C. The cod is ready when the skin is golden and the meat flakes easily. The caramelized onion will have absorbed some of the cod's juices, creating a dark, sweet, and deeply flavorful sauce that is the true star of the dish.
- Serve directly from the dish, with the onion as a base and the cod on top. It needs no other accompaniment than crusty bread to soak up that dark, addictive sauce from the bottom.
The house trick
Patience with the onion is non-negotiable. If you turn up the heat to go faster, the onion fries instead of caramelizing, and the flavor is completely different: bitter and dry instead of sweet and silky. Thirty minutes over low heat are non-negotiable if you want the correct result. You can caramelize the onion the day before and store it in the fridge. The next day you just have to assemble the dish and bake it.
Buy it at BacalaloExtra Desalted Clean Cod Loin - 900g€44.90 · 24-48h refrigerated shipping →Frequently asked questions
How to properly poach onions?
Over low heat and with patience (20-30 min), with a little oil and salt, until they are transparent and sweet. Rushing burns them instead of sweetening them.
How much oven time does cod need?10-15 minutes at 190 °C over the already poached onion, just enough for the cod to be juicy.
Does it contain pepper or tomato?
It allows for variations: a little pepper or tomato enriches the base, but classic "encebollado" shines with just onion and good oil.
