Mayonnaise from Scratch

Homemade mayonnaise is an emulsion: egg yolk holds together oil and vinegar that would otherwise separate, with mustard providing extra emulsifying power. The technique is patience. Whisk one yolk with a teaspoon of mustard, salt and a splash of vinegar or lemon, then drizzle in oil — at first literally drop by drop — while whisking constantly. Once the mixture thickens, the oil can go in faster in a thin stream. Adding oil too quickly is the most common failure: the emulsion breaks and you have a greasy yellow puddle. To rescue split mayo, start a fresh yolk in a clean bowl and slowly whisk the broken mix into it.