Culinary Notes
The Emulsion Rule: When making it from scratch, the oil must be added drop by drop initially while whisking vigorously. If you add the oil too quickly, the emulsion will "break" or split, resulting in a greasy, separated liquid rather than a thick cream.
The Rescue Mission: A broken mayonnaise can always be saved. Start with a fresh egg yolk (or a teaspoon of Dijon mustard and a splash of boiling water) in a clean bowl. Slowly whisk your broken, greasy mixture into this new base, drop by drop, until it re-emulsifies into a thick sauce.
The Golden Crust Trick: Spreading a thin layer of mayonnaise on the outside of a grilled cheese sandwich or a piece of poultry before searing is a chef's secret. Because mayo is an emulsion of oil and egg protein, it creates a perfectly even, golden, and crispy Maillard crust without burning as quickly as whole butter.
The Temperature Factor: All ingredients (eggs, mustard, oil, and acid) should ideally be at room temperature before you begin whisking. Cold egg yolks are stiff and struggle to absorb the oil effectively, increasing the risk of the sauce splitting.