The New Zealand Railways Magazine, Volume 13, Issue 11 (January 1, 1939)
A well made sauce should be free from lumps, have a glossy appearance and velvety smoothness.
Add liquid gradually and stir all the time the sauce is cooking.
Boil from three to five minutes, and then beat well until smooth and glossy.
One oz. butter, one hard-boiled egg, one oz. flour, one breakfastcup milk, pepper and salt. Take the yolk of the egg and with a fork work it into the flour until quite free from lumps. Melt butter in saucepan. Remove from the fire and work in flour and egg yolk until quite smooth. Add milk gradually and stir until boiling. Add pepper and salt and the roughly chopped white of egg.