Mix together the sugar and egg yolks or whole egg. Warm the milk until about at blood heat. Stir the milk into the egg, return the whole to the rinsed pan and cook gently until the egg thickens, without boiling or the egg will curdle. At once pour out of the pan into a basin or the sauceboat. Flavour and add extra sweetening if required. If the custard should curdle, whisk it vigorously just before serving.