In your Vitamix blender add eggyolks, dry mustard, and lemon juice and blend on high.
Turn machine down to low, remove top and slowly pour in the melted butter.
Put top back on blender and turn machine to high again and blend until smooth.
Add the cayenne and salt.
I served this right away on the hot asparagus.
You can keep the hollandaise warm in a double boiler or in a small crockpot on very low heat.