Know the structure
An emulsion disperses one liquid in another that normally separates from it. In a warm butter sauce, water and butterfat need help staying evenly combined. Whisking, enough liquid and controlled heat are more useful than simply adding extra butter.
Begin with a flavorful liquid
Use a small cooked reduction of stock and a little lemon or vinegar, following a butter-sauce recipe. Keep some liquid in the pan: a completely dry pan cannot provide the water phase. Have cold butter cubes and a whisk ready before beginning the finish.
Mount gradually
Lower the heat or remove the pan from the burner. Whisk in small pieces of cold butter a few at a time as each becomes incorporated. Aim for a cohesive, creamy-looking sauce rather than a boiling pool of fat. Alternate brief gentle warming with whisking off heat when needed.
Recognize a break
Visible oil pooling means the sauce is separating. Remove it from heat and try whisking in a small splash of water. If necessary, start a fresh spoonful of warm water in another pan and slowly whisk in the broken sauce. Serve promptly; this lesson uses no raw egg.
Your next kitchen exercise
Finish a spoonable stock-and-lemon sauce with cold butter, using a specific recipe for amounts. Note the texture before and after whisking.
