I've always intended to try this one but have never gotten around to it.
https://www.allrecipes.com/recipe/84214/blender-hollandaise-sauce/
"The easiest way to get perfect Hollandaise sauce is to use a blender. This recipe has all the same ingredients as the classic, but no double boiler and no chance of the sauce separating. I love the lemony flavor on fresh steamed asparagus!"
Ingredients
3 egg yolks
1/4 teaspoon Dijon mustard
1 tablespoon lemon juice
1 dash hot pepper sauce (e.g. Tabasco(TM))
1/2 cup butter
Directions
In the container of a blender, combine the egg yolks, mustard, lemon juice and hot pepper sauce. Cover, and blend for about 5 seconds.
Place the butter in a glass measuring cup. Heat butter in the microwave for about 1 minute, or until completely melted and hot. Set the blender on high speed, and pour the butter into the egg yolk mixture in a thin stream. It should thicken almost immediately. Keep the sauce warm until serving by placing the blender container in a pan of hot tap water.