Put 1 large pasteurized egg yolk (at room temperature), 1 teaspoon Dijon mustard, and 1 3/4 teaspoons fresh lemon juice into a medium bowl. Whisk until smooth and combined.

Begin adding 1 cup avocado oil very slowly while whisking vigorously: start with just a few drops of oil and whisk until those drops are fully incorporated and the mixture starts to thicken.

Once the emulsion has started, continue adding the oil in a thin, steady stream while whisking constantly until all the oil is incorporated and the mayonnaise is thick and glossy.

Stir in 1/8 teaspoon salt, taste, and adjust seasoning by adding more salt if desired.

Transfer the mayonnaise to a clean container, cover, and chill in the refrigerator before using.