You can rescue it by starting the process again, with an egg yolk in a bowl over a bain-marie which you whisk until it starts to thicken a little. then incorporate a little warm melted butter into the egg yolk.
Once this is incorporated you can slowly start to add the split hollandaise and this should then incorporate into the new base, unsplit.
There is a video here
cooking.stackexchange.com/users/210/Sam Holder
Jacques Pepin, in his book "Complete Techniques", recommends to try first save the mixture as soon as you see it starts getting oily around the edges, by adding a tablespoon of cold water or an ice cube and beating well.
If that doesn't save it, then: Separate the mixture completely by stirring over heat.
Tilt the pan and let rest for 5 minutes
so the oily part comes to the top whereit can be removed (but don't discard).
Start with 2 tsp of warm water in a bowl and add 1 tbsp of the thick sauce at a time, whisking in until smooth at each addition.
Start adding back in the oily part, beating it in like you were making the sauce from the start.
If any parts have scrambled, put through a strainer.
cooking.stackexchange.com/users/8315/jontyc
This technique works well.
If your sauce starts to split take the pot off the heat immediately and put he entire pot in the sink in an inch of ice cold water to cool it quickly.
Add a tsp of ice cold water to the sauce and whisk vigorously.
May have to add a 2nd tsp but don't add too much at once.
If you find your sauce splitting often try a little lower heat or a copper pot for better heat distribution.
To hold the sauce at temp a thermos works well.
cooking.stackexchange.com/users/46/Foodie Ron
What I do is to take the pot off the heat, then put a clean pot on the heat and add between a tea spoon and a table spoon of lemon juice.
Then gradually add the split sauce from your original pot a table spoonful at a time, or at a very slow trickle.
Whisk the sauce all the time.
It works like a charm.
cooking.stackexchange.com/users/1720/Martin Duys
We put it back in the blender and pulsed a few times.
Good as new!
cooking.stackexchange.com/users/42612/Laura Sebly
If a sauce has separated, take it off the heat, throw in an ice cube, stir.
Saved me many times.
cooking.stackexchange.com/users/746/paprika
Add a splash of cold milk and whisk.
It is smooth and glossy within seconds.
cooking.stackexchange.com/users/26687/Bob
I made a hollandaise sauce on the weekend and it split so I threw it out and started again but I was wondering if there is anything you can do to save it once it splits?
How can I fix a hollandaise sauce after it has split?
cooking.stackexchange.com
<sauce><hollandaise>
cooking.stackexchange.com/questions/728
cooking.stackexchange.com/users/125/lomaxx
Remove from the heat and add a teaspoon of water, cold milk or an ice cube as soon as it starts separating, then beat well. You can also restart the process by whisking an egg yolk over a bain-marie until thickened, then adding a little warm melted butter. You can also pulse it in a blender a few times to recombine. You can add some melted butter and another egg yolk. Alternatively, add some cold water, cold milk or an ice cube.
Add some melted butter to an egg yolk and add in. Add some cold water or an ice cube. Blend for a few seconds. Add some cold milk.