Vanilla custard is the classic accompaniment to British steamed puddings, but scrambled eggs lurk as an ever-present threat. The safeguard is tempering: slowly raising the temperature of the egg yolks before they meet the full heat of the cream. Pour the hot cream in a thin, steady stream into the egg mixture while whisking constantly—this gradually warms the eggs without cooking them. The cornstarch in the mixture provides additional insurance against curdling. Once combined and returned to the pan, stir constantly over low heat until the custard coats the back of a spoon and holds a line drawn through it. Never let it boil. Strain through a fine sieve for silky results.