If milk or eggs curdle or if you curdle them, they separate into different bits. The sauce should not boil or the egg yolk will curdle The herb has been used for centuries to curdle milk
some sauces and other mixtures can separate In baking this is particularly common when adding eggs or other liquid to a creamed mixture (see above) To stop this, add a tablespoon from the weighed flour after the first egg or couple of spoonfuls of liquid