Gradually the mixture will begin to turn colour.

As soon as this turn of colour is perceptible take out half and put it in a basin.
This is the white roux, viz., flour cooked in butter but not discoloured beyond a very trifling amount.

Keep the stew-pan on the fire, and go on stirring the remainder, which will get gradually darker and darker in colour.

As soon as the colour is that of light chocolate remove the stew-pan from the fire altogether, but still continue scraping and stirring for a few minutes longer, as the enamel retains the heat to such an extent that it will sometimes burn after it has been removed from the fire.

It is important not to have the mixture too dark, and it will be found by experience that it gets darker after the stew-pan has been removed from the fire.