Many people might think it’s impossible to whip garlic, salt and olive oil into a satiny, mayonnaise-like sauce, but then they have never seen a Catalan cook prepare ali-oli. This pungent condiment, a cornerstone of the Catalan kitchen, presents a mystery to anyone accustomed to making mayonnaise, an emulsion of oil and egg. What makes ali-oli so thick? What holds it together? How can you make a stable sauce without egg?

The answer lies in the steady hand of the cook and the ability of the moist mashed garlic and olive oil to emulsify. Adding the oil drop by drop and stirring constantly with a wooden pestle (this is a mortar task, not one for the food processor), the cook achieves a thick, silky, homogeneous sauce imbued with garlic fragrance. This potent mixture is not for the fainthearted. And it is not mayonnaise. It is ali-oli, whose very name translates as garlic (all) and (i) oil (oli).

Ali-oli stays in the inverted bowl
In Catalonia, ali-oli is an all-purpose accompaniment. It appears with paella and other rice dishes, with boiled shellfish, seafood soup, grilled or salt-baked fish, grilled pork, and the chile-spiked fried potatoes known as patatas bravas.

Admittedly, making an authentic ali-oli, without egg, is a technical feat that takes practice to master. That’s why many people, even professional chefs, add a little egg to the pounded garlic before incorporating the oil. Purists would say it’s no longer the true ali-oli, but most Catalans are not bothered by that technicality. Ali-oli made with egg is quick, foolproof and a rich golden color. In modern kitchens, it has largely replaced the original. Some eggless versions call for a little boiled potato or bread to help the emulsion along, but that, too, is controversial. Whether made with egg or without, with potato or not, ali-oli should be stiff—some say so stiff that it won’t fall out if you invert the mortar. But that may be a test you don’t want to try.

When making ali-oli, choose a mild extra virgin olive oil, or cut a peppery extra virgin with pure olive oil. Be sure to pound the garlic with salt to a fine paste before adding the egg (if using) and the oil. Some people like to brighten the sauce at the end with a little lemon juice or white wine vinegar; others consider any addition unacceptable.

Watch Josep Maria Blassi prepare ali-oli in a mortar the old-fashioned way—with no egg. (Flash video, 6:38)

Put a bowl of ali-oli on the table to enhance any dish that can use a garlicky boost. It’s superb with many vegetables: roasted asparagus, steamed artichokes, boiled potatoes, sliced tomatoes, grilled mushrooms, grilled leeks. Add a generous spoonful to mashed potatoes in place of butter, or dollop on a baked potato. Steam mussels or clams, then whisk some of the pan juices into ali-oli to thin it and drizzle over the hot shellfish.

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