Cut into little squares the half of a carrot and a small onion; take a small saucepan, put in a good bit of butter, add the vegetables, fry them lightly without letting them brown. This done, add a good tablespoonful of flour, and let the flour cook quite gently for several minutes on a moderate fire; be especially careful that it does not stick or get coloured, which would quite spoil its quality. This done, let it cool for a moment, then add little by little one pint and a half of boiling milk; work and stir the sauce without ceasing until it boils, remove to side of a slow fire, and let it cook for an hour. Strain the sauce through a flannel or muslin into a bain-marie, with a pinch of salt, and of grated nutmeg very little. Add a good bit of butter while working it with a small egg-whisk. The sauce should be very smooth, creamy, and of a good flavour; if by chance it is too thick, this can be remedied by adding a few spoonfuls of good, thick, and sweet cream.