Or the same thing in a bowl with a whisk. There's no need for any double boilers or other elaborate technique.

Or the same thing in a food processor. Except I don't use the hot sauce. Nor do I let the butter cool. I process three egg yolks with some lemon juice. Melt a stick of butter and slowly drizzle it in while the processor is running. Then use the sauce when needed, without reheating. Even if you have sauce leftover, and you've put it in the refrigerator, the warmth of whatever you are using it on is sufficient to "remelt" it.

I cheat and use a blender -- melt 8-tbls butter and set aside to cool a bit. In a blender combine, 3 egg yolks, 1-tbl plus 1-tsp fresh lemon juice or white wine vinegar. 1/4-tsp hot sauce. Increase speed to medium and slowly drizzle in the melted butter to make the hollandaise. Ta Da.