Not just a sauce; an allemande by Johann Jakob Froberger

Marie Antonin Carême (author of the encyclopedic, L’Art de la Cuisine Française, 1834) categorized all sauces as belonging to one of the five “Mother Sauces“, Sauce Allemande is from velouté sauce, a blond sauce of veal (or chicken) stock thickened with a roux of butter and flour. Later on, Escoffier (A Complete Guide to Modern Cookery) added a few mother sauces and further normalized preparations. I can find no mention of Sauce Allemande before Menon (Nouveau Traité de la Cuisine, etc.), Marin (Les Dons de Comus) and Le Cuisinier Gascon – this isn’t terribly surprising, as there is a gap in French cookbooks between La Varenne’s mid 17th century works and these:

Menon Nouveau Traité de la Cuisine, 1739

Sauce à l’Allemande.
Mettez dans une casserole. une tranche de Jambon que vous faites suer & un peu attacher : mouillez-la avec du bouillon &c du coulis : faites-la bouillir: quand elle eft réduite & dégraiflëe, paflez-la au tamis Se mettez dedans des soyes & persil blanchi , & hachez câpres & anchois ; hachez deux ciboules entieres , deux pains de beurre de Vambre ; faites lier la sauce furie feu , qu’elle ne foit pas trop épaifle ; ôtez le ciboules & mettez-y un peu de gros poivre , & le jus d’un citron.

Put in a casserole. a slice of ham that you sweat & just attach: moisten it with broth: boil it: when it is reduced & deglazed, pass it to through a sieve. With the blanched parsley, mill & chop capers & anchovies, chop two whole onions, two kilos of fresh, sweet butter [literally butter from Vanvres, an 18th century delicacy]; add the butter to the sauce with the fire raging, when not too thick, remove the onions & put it a little coarse pepper, and the juice of a lemon.

A Mention of Sauce Allemand in Oeconomische (Oekonomisch-technologische) Encyclopädie, oder allgemeines ... By Johann Georg Krünitz 1811

The cook’s dictionary, and housekeeper’s directory by Richard Dolby, 1833
Sauce à Г Allemande.*—Put a slice of ham, and some champignons (previously dressed and shred) into a stewpan ; set it on the fire, and when the ham begins to stick, moisten it with stock and consamie, boil and reduce it ; then take off the fat, strain the sauce, and add to it some scalded parsley, two fat livers, capers, anchovies, scalíions, all chopped, add a bit of butter, put it again on the fire, and when of the requisite consistence, take out the scallions, put in some migncmette and lemon juice, and strain it for use.

La grande cuisine simplifiée,: art de la cuisine nouvelle mise à la portée … By P. C. Robert, 1845

Sauce allemande.
Mettez dans une casserole sur le feu 3 cuillerées de velouté, une de consommé, faites réduire à point; mettez-y une liaison de 2 jaunes d’œufs, gros comme un œuf de bon beurre, un petit jus de citron; passez votre sauce à l’élamine et tenez-la chaudement au bain-marie jusqu’au moment de l’employer.

Put in a saucepan on the heat 3 tablespoons of sauce velouté , 1 tablespoon consommé, just so; make a liaison with 2 egg yolks, as big as an egg of good butter, a little lemon juice, pass your sauce through a strainer [I think élamine is just a highly technical term for sieve] and keep it warm in a bain-marie until ready to use.

Escoffier, A Complete Guide to Modern Cookery, 1908

Allemande Sauce is not, strictly speaking,, a basic sauce. However, it is so often resorted to in the preparation of other sauces that I think it necessary to give it after the Veloutes, from which it is derived.
Quantities Required for One Quart.

The yolks of 5 eggs. the juice of a lemon.
1 pint of cold white stock. pint of mushroom liquor.
1 quart of Veloute, well despu-
mated. .

Mode of Procedure.—Put the various ingredients in a thick-bottomed saute”-pan and mix them carefully. Then put the pan on an open fire, and stir the sauce with a metal spatula, lest it burn at the bottom. When the sauce has been reduced to about one quart, add one-third pint of fresh cream to it, and reduce further for a few minutes. It should then be passed through a fine strainer into a tureen and kept moving until quite cold.

Prepared thus, the Allemande Sauce is ready for the prepara tion of the smaller sauces. Butter must only be added at the very last moment, for if it were buttered any earlier it would most surely turn. The same injunction holds good with this sauce when it is to be served in its original state; it should then receive a small addition of cream, and be buttered so that it may attain its required delicacy; but this addition of butter and cream ought only to be made at the last moment, and away from the fire. When a sauce thickened with egg yolks has any fat substance added to it, it cannot be exposed to a higher tempera ture than 140 degrees Fahrenheit without risking decomposition.

The Picayune Creole Cook Book, 1922
Sauce Allemande
4 Pounds of Raw Veal.
The Bones of a Chicken.
1 Gallon of Water.
1 Carrot.
1 Turnip.
Celery Tops.
2 Tablespoonfuls of Butter.
2 Spoonfuls of Lard. 1 Herb Bouquet of Thyme, Parsley, Bay Leaf. 1 Stalk of Celery. 2 Long Carrots.

Take the veal and the bones of the chicken and put into a pot with a gallon of water. Add the herb bouquet, tied together, and one chopped carrot, one turnip, chopped, celery tops, and other ingredients of a good “pot-au-feu.” Let all boil slowly for three hours until it is reduced onehalf. Then salt and pepper to taste. This will give a white broth or consommé blanc. When boiled to this point take off the fire and strain the broth into a jar. Now put two tablespoonfuls of butter and three of flour. into a saucepan together, letting the butter and flour blend nicely, without browning. Add all the broth to this, stirring slowly while on the flre. Add a good, strong bouquet of herbs, Ihyme, parsley and bay leaf, all tied together whole. Add two large carrots, letting all boil till reduced to one-half again. After this process, season to taste, and when It has reached the consistency of starch take it from the fire, strain, and let it get cool. This sauce is fine for all white meats and fish. When used for fish take one tablespoonful and moisten with a little fish broth. Set on the fire to heat, and add a pint of consommé or broth. This sauce Allemande will keep at least one month in our climate, in the ice box. If one prefers to make it as needed, follow the proportions of one tablespoonful of butter, two of flour, and one pint of boiling broth.