This section is from the book "The Epicurean", by Charles Ranhofer. Also available from Amazon: The Epicurean, a Complete Treatise of Analytical and Practical Studies on the Culinary Art.
In order to make thick stock use consomme of game, vegetables, fish or chicken before they are clarified. Place half a pound of butter in a saucepan with half a pound of sifted Hour of the best quality, let cook well on a slow fire without coloring when needed for vegetables, fish or chicken, but for game make a brown roux; for either one or the other dilute this roux with boiling broth (if the soup should be a chicken soup, chicken broth should be used to dilute the roux, if game soup then game broth should be used, fish with fish broth, for vegetable, vegetable broth). Use a whisk turning it rapidly, so as to avoid having lumps; stocks for soups should be kept rather thin, that is to say but little thickened and should be well despumated, the fat removed before passing through the tammy; return the saucepan to the fire, and stir continuously with a spatula from the bottom until the broth boils. Remove the saucepan and place it so that only one side of the contents cook slowly for one hour;'skim and take off all the matter that swims on the surface until the stock be entirely free from fat, and other impurities floating on top arising from the clarification, then strain through a tammy or fine sieve, and use this stock for thick soups either of game, vegetables, fish or poultry.