Peruvian Ají Amarillo Beurre Blanc for a Whole Roasted Fish
The classic French butter sauce meets the fruity heat of Peru's national chilli. We developed it for a whole roasted sea bream, but it will make a hero of any white fish, a grilled leek or a plate of new potatoes.
- 1 whole sea bream or sea bass, about 1 kg, scaled and gutted
- 1 lemon, thickly sliced
- Olive oil, sea salt
- For the sauce: 100 ml dry white wine
- 2 tablespoons white wine vinegar
- 1 shallot, finely chopped
- 2 tablespoons ají amarillo paste
- 200 g cold unsalted butter, cubed
- Juice of half a lime
- Salt to taste
- A few coriander leaves
- Heat the oven to 220 C. Lay the lemon slices on a tray, set the fish on top, score the skin, rub with oil and salt. Roast for 25 to 30 minutes until the flesh flakes at the thickest point.
- Meanwhile, put the wine, vinegar and shallot in a small pan and reduce over medium heat to about 3 tablespoons of liquid.
- Whisk in the ají amarillo paste and cook for 1 minute more.
- Lower the heat to its minimum. Add the cold butter two or three cubes at a time, whisking constantly, letting each batch melt before adding the next. The sauce must stay warm, never boil.
- When all the butter is in, season with lime juice and salt. Strain if you want it perfectly smooth; we leave the shallot in.
- Pour half the sauce over the fish at the table, scatter the coriander, and serve the rest in a warm jug.
Beurre blanc is one of the great sauces of the French kitchen and one of the least forgiving: a reduction of white wine, vinegar and shallot into which cold butter is whisked until it emulsifies into something glossy and ivory. Get it too hot and it splits; leave it too cold and it sets. Peru's ají amarillo, a bright orange chilli with a tropical, almost mango-like flavour and a medium heat, turns out to be the ideal partner for it. The chilli's fruit does the job of the shallot's sweetness and its heat cuts the butter.
In Lima, ají amarillo is the base of a dozen sauces, from the cheese-thickened huancaína to the walnut ocopa. It is usually blended into a paste, which is exactly how we use it here: the paste is whisked into the reduction before the butter, so the emulsion is built around it rather than stained by it afterwards. The finished sauce is a saturated golden yellow and tastes of butter first, then fruit, then a slow warmth at the back of the palate.
Choosing the fish
A whole sea bream or sea bass of about a kilo, scaled and gutted, roasted on a bed of thick lemon slices, gives you the sweet flesh this sauce needs. Score the skin three times on each side so the salt gets in. If you cannot find ají amarillo paste, blend two fresh yellow chillies with a spoon of water; the sauce will be sharper but still good.
On serving
Bring the fish to the table whole on its roasting tray and pour half the sauce over the top just before it goes down, so the skin glistens. Keep the rest warm in a jug. Boiled Peruvian purple potatoes, halved and dressed with olive oil, are the right thing beside it. A cold Sauvignon Blanc or a Peruvian pisco sour both work; the second is more fun.