Thicken the sauce with a little butter and flour, or white roux, and season with pepper and salt.

A very nice mild onion sauce is made by using Spanish onions.
ONION SAUCE, BROWN .-- Slice up half a dozen good-sized onions; put them in a frying-pan and fry them in a little butter till they begin to get brown, but be careful not to burn them, and should there be a few black pieces in the frying-pan, remove them; now chop up the onions, not too finely, and put them in a saucepan with a very little stock or water, let them simmer till they are tender, and then thicken the sauce with a little brown roux, and flavour with pepper and salt.
ORANGE CREAM SAUCE FOR PUDDINGS .-- Take a large ripe orange and rub a dozen lumps of sugar on the outside of the rind and dissolve these in a small quantity of butter sauce, and add the juice of the orange, strained.

Now add a little cream, or half a pint of milk that has been boiled separately, in which case the sauce will want thickening with a little white roux.
Rubbing the sugar on the outside of the rind of the orange gives a very strong orange flavour indeed--far more than the juice of almost any number of oranges would produce, so care must be taken not to overdo it.

This is what French cooks call zest of orange.
PARSLEY SAUCE .-- Blanch and chop up sufficient parsley to make a brimming tablespoonful when chopped.

Add this to half a pint of butter sauce, with a little pepper, salt, and lemon juice.