Custard Sauce

In case you'd like to try this on your apple crisp, here's a British
recipe for custard sauce - just keep stirring! It's used on many
desserts, from stewed fruit to steamed puddings and often pies. Hope
that helps.

Custard Sauce

1-1/2 cups milk
2 egg yolks
1 oz. castor sugar (it's just very fine sugar)
2 or 3 grains salt (I don't count them!!!)
1/2 teaspoon vanilla

Beat the egg yolks slightly in a basin. Stir in the sugar and salt.
Bring the milk to boiling point in the top of a double boiler with
water boiling below, then pour, *a few drops at a time*, into the
beaten egg yolks, etc., stirring constantly until all the milk is
added. Turn back into the top of the double boiler. Cook, stirring
constantly, until the mixture thickens. Stir in the vanilla.
Note: 1) Do not allow the custard to boil.
2) The mixture should be just thick enough to coat the
back of a spoon.

Source: rec.food.cooking