Stovetop Method: Melt the butter until it's not just melted but HOT. (Be sure to cover the bowl because butter splatters!) Vigorously whisk the egg yolks and lemon juice or white vinegar in a stainless steel bowl until thickened. Place the bowl over a small saucepan with simmering water, ensuring the bowl is ABOVE the water and not touching it, to prevent scrambling. Continue to whisk the eggs while drizzling in the hot melted butter in a slow, steady stream until the sauce has thickened. If you prefer it thinner, add a teaspoon or so of water. Be careful not to let the sauce overheat. Remove the bowl from the heat and whisk in the salt and cayenne pepper if using. Taste and add more salt if desired. Serve immediately. If waiting, keep warm by covering and placing in a warm spot (next to the stovetop, over a double boiler, or over a small saucepan containing hot water, again ensuring no contact with the water).

Blender Method: Melt the butter until it's not just melted but HOT. (Be sure to cover the bowl because butter splatters!) Place the egg yolks, lemon juice, salt, and cayenne pepper (if using) in a blender and blend on medium for about 5 seconds until combined. Remove the plug from the blender lid and, with the blender on medium, slowly pour in the hot butter in a steady stream. Continue to blend until the sauce is emulsified and thickened. If you prefer it thinner, add a teaspoon or so of water and blend. Taste and add more salt if desired. Pour the hollandaise sauce into a bowl and serve immediately. If waiting, keep warm by covering and placing in a warm spot (next to the stovetop, over a double boiler, or over a small saucepan containing hot water, again ensuring no contact with the water).