Ensure all ingredients are at room temperature. This helps in achieving a smooth emulsion.
In a medium bowl, whisk together the egg yolks and mustard until well combined.
Slowly whisk in the vinegar or lemon juice. This will help stabilize the yolk mixture.
Begin adding the oil very slowly, almost drop by drop, while continuously whisking. This step is crucial to form a stable emulsion. As the mixture thickens, you can add the oil a bit more quickly.
Once all the oil is incorporated and the mayo is thick and creamy, season with a pinch of salt. Taste and adjust the seasoning as needed.
If desired, add minced garlic, chopped herbs, or your favorite spices to customize the flavor.
Transfer the mayonnaise to a clean jar or airtight container.