If a Hollandaise sauce curdles, take it off the heat and beat in 1 tablespoon of cold water, a little at a time, until the sauce becomes smooth. Alternatively, stir an ice cube into the warm sauce. If this doesn't work, beat an egg yolk in a clean pan over a low heat until it thickens. Then gradually beat in the curdled sauce until smooth.
Rescue a lumpy sauce or gravy by whisking it hard in the saucepan. If this fails, whizz the sauce in a blender, or rub it through a sieve.
A custard sauce curdles if allowed to boil or cooked over a high heat too fast. Immediately put the saucepan into just enough cold water to cover the base. Then stir in 2 teaspoons of cornflour for every 1 pint/ 570ml of custard. Alternatively, pour the custard through a sieve into a clean bowl and cool it quickly by placing the bowl in cold water.
Save a sauce that is too sweet by adding a little lemon juice.
Prevent sauce from burning or setting at the bottom by whisking it rapidly in a figure-of-eight motion.
Simmer sauces if you want to reduce them - never boil them or they may curdle or cloud.
If you need to leave a white sauce standing, coat the surface while still warm with a lump of butter to prevent a skin from forming.
