In brown roux each grain of flour is cooked till it is done brown.

We cannot exaggerate the importance of getting cooks to see the enormous difference between thickening soups or gravy with white or brown roux and simply thickening them with plain butter and flour.
The taste of the soup in the two cases is altogether different.

The difference is this.

Suppose you have just been making some pastry--some good, rich, puff paste--you have got two pies, and, as you probably know, this pastry is simply butter and flour.

Place one pie in the oven and bake it till it is a nice rich brown.