Aioli is the pungent garlic sauce of Provence and the Catalan Mediterranean, made by pounding raw garlic to a paste and working olive oil into it drop by drop until it thickens into a glossy, stiff emulsion. In its oldest form it is nothing but garlic, olive oil and salt — a fiercely garlicky cousin of mayonnaise that carries the flavour of raw garlic and fruity oil rather than egg and neutral seasoning.