¼cupvegetable oil or other lightly-flavored oilMaybe melted coconut oil?
¼cupextra virgin olive oil
2Tablespoonswhey from yogurt
Crack the egg into a wide-mouth canning jar and add the lemon juice. Whip together and let sit until it gets close to room temperature - about 5-10 minutes.
Add the salt, pressed garlic & 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 it will keep several weeks but I've never had it long enough to test that. Let me know how long your mayonnaise lasts!