Ingredients
3 egg yolks
1/3 tsp Dijon mustard
1 tbsp lemon juice
dash hot pepper sauce
dash of salt
1/2 cup melted butter, keep hot
Steps

1. Put egg yolks, mustard, lemon juice, pepper sauce, and salt in a blender.
2. Blend for about 5 seconds or so.
3. Turn on blender to high, pour in hot melted butter slowly in a thin stream from the top of the blender.  
4. Stop the blender and check for consistency.  It should already be thick.  
5. If you need to keep it warm, place the blender pitcher in a bowl or pot of warm water.