Ingredients:
3 (preferably local) egg yolks at room temperature
3/4 cups of butter, unsalted
1 – 1 1/2 tablespoons fresh lemon juice
1 teaspoon dijon mustard
pinch of cayenne
Method:
Melt butter in a small saucepan.
Place the eggs, lemon juice, cayenne and mustard in a blender. Blend for a minute until nicely combined.
Pour the butter through the hole in the top of the lid of the blender, SLOWLY, with the blender at high speed. This should take about 10-15 seconds to blend and thicken. You will hear the change as it thickens. Trust me, you’ll know.
Source: http://localmilkblog.com/