Homemade mayonnaise is easy to make. I sometimes flavor it with garlic - something RancherMan loves. #TexasHomesteader
Add the salt, pressed garlic (if making flavored mayo) & mustard powder.
With an immersion blender at the bottom of the jar start blending, then in a VERY THIN STREAM and very slowly pour in the oils. The ingredients will emulsify about halfway through but keep pouring slowly until all oil is incorporated. This should take about 3-4 minutes total.
Finally add in the whey and blend together. Store in the refrigerator.
We go through our mayo pretty quickly so I don't really know how long it will keep, I've read that by adding the whey the mayo will keep several weeks in a closed container in the refrigerator. But we use it fast enough that I've never had occasion to test that. Let me know how long your mayonnaise lasts!