I know how to fix a split mayonnaise made with olive or vegetable oil - that's not a problem.
I have made Kenji Lopez-Alt's recipe for animal fat mayonnaise (bacon fat, for putting on a burger). It emulsified beautifully, chilled wonderfully.. and then as soon as you put it on a burger it gets too warm and splits faster than a gymnast at the Olympics.
The recipe I used:
2 egg yolks
1tbsp white wine vinegar
salt and pepper
600mL bacon fat
800mL vegetable oil
Two egg yolks should be more than enough to emulsify this, and indeed were -- I had to add tons of vegetable oil just to get the right consistency. But as soon as the bacon mayonnaise gets above fridge temp, it splits immediately. It re-emulsified with agitation, but that's a bit tough to do when one is trying to serve a burger in a restaurant. Help?