1/4+ 1/8 teaspoon saltor 1/2 if using unsalted butter
2 teaspoons prepared mustard
Using a whisk, blender, or stick blender, blend the egg, lemon juice, salt, and mustard until smooth.While blending, slowly add the melted butter. Watch out for splatters! Continue blending until the mayo gets thick.
Use immediately and store any leftovers in the refrigerator for about a week. Soften mayo by placing jar in some warm water.