Melt and cool butter to room temperature first.
Separate egg yolks, then place in a blender.
Add dijon mustard, lemon juice and salt.
Blend on high for about 15 seconds.
Turn the blender on low. While it's running, add the butter in a slow, steady stream.
Keep blending until a thick sauce forms.
Serve over eggs, vegetables, or really anything else. Hollandaise will keep in the fridge for about 5 days.