Credit to Chef John for this recipe which is easy and tasty with fish.

• 15ml or Tbsp Lemon or White wine vinegar
• 250ml or Cup White Wine
• 2 Tbsp cream (it helps stabilise )
• 2 tsp fine dice shallot
• 120g cold butter in cubes
• Chopped Parsley or chives

Put wine, lemon and shallot in a pan and reduce by 75%. Whisk in the butter a few cubes at a time.  See it thicken as you whisk and the liquid and butter form emulsion. Finally, add the chopped parsley or chives.

Spoon over asparagus or pan fried/grilled fish.