Milk was an important ingredient in medieval cookery. The problem with animal milk (milk from cows, goats, and sheep) was that it had a very limited shelf life. Also, the taste and quality of milk changed with the seasons and with the feed of the animals. Add to that the fact that animal milk was prohibited on fast and lean days. To get around these issues, medieval cooks turned to other sources for milk. Almonds, as well as hazelnuts and walnuts, can be turned into a milk-like substance.
Like animal milk, almond milk can by churned into butter, can thicken sauces and carry fat soluble flavors. Since it contains no animal products, almond milk could be enjoyed on fast and lean days and during Lent. Almond milk also had a more consistent flavor than animal milk and does not spoil easily. It could be made as needed and any excess could be stored for several weeks. While it was an ingredient in many dishes, almond milk was also consumed just like animal milk; by the glass. It was recommended, by physicians, as “blessed with qualities that were very close to the healthy human temperament”  and was prescribed for those who were sick or had digestive problems.
From Du fait de cuisine:
28. And again, flans of almond milk: according to the quantity of flans which you are making take the quantity of almonds, have them well and cleanly blanched and washed and then have them very well brayed; and take very clean fair water and let him strain his almond milk into a bowl or a cornue which is fair and clean according to the quantity of flans which he should make….
From Le Viandier de Taillevent:
Take peeled almonds, crush very well in a mortar, steep in water boiled and cooled to lukewarm, strain through cheesecloth, and boil your almond milk on a few coals for an instant or two.
The redaction from A Boke of Gode Cookery
1 cup ground almonds
2 cups boiling water
Combine almonds and water. Steep for 5 minutes, stirring occasionally. Sieve the mixture to remove coarse grains OR (preferably) blend mixture in electric blender until grains are absorbed. Yield – 2 cups almond milk.
The redaction from Medieval Cookery
2 cups blanched almonds
3 cups hot water
Grind almonds until fine, almost like flour. Pour hot water into almonds, mixing well. Allow to soak for 10 to 15 minutes, stirring occasionally. Pour through a fine strainer into a bowl, discarding solids (they can be used again with more water, but the resulting almond milk will be thinner and won’t work as well in recipes)
My method is as follows:
1 cup whole, blanched almonds
2 cups boiling water
Grind the almonds by hand, using a mortar and pestle: grind until you end up with a gritty paste. This will take a while, but the finer the paste is, the better the end result will be. Once you have achieved paste, set two cups of water to the heat and bring it to a rolling boil. Once you have a rolling boil, add the almond paste and take the water off of the heat. Let the mixture steep for ten minutes, stirring every few minutes. After ten minutes, Strain the mixture through cheesecloth, make sure to squeeze all of the liquid from the cloth. Be careful, the liquid will hot. Cover the almond milk and let it cool on the counter. Once cool, feel free to drink the milk or use it for cooking. In a sealed container, your almond milk will last about a week on the counter, or up to three weeks in the ‘fridge.
By following this method you will end up with something with the taste and consistency of almond-flavored skim milk, and while it can thicken a sauce like milk or cream, it doesn’t do it as well or as quickly. Also, the almond flavor doesn’t cook out. Further, almonds have no sugar, so almond milk isn’t sweet like cow or goat milk. Modern, mass-produced almond milk is not the same thing as our period product: they are vitamin fortified, with extra fat, sugar and emulsifiers added to give them the flavor, and mouth-feel, of cow milk.
A purely modern method would be to put a cup of blanched almonds in a bar blender with two cups of hot water and blend until smooth. The bar blender will whip air into the mixture and pulverize the almonds, releasing more of the drupe’s natural emulsifiers, thickening the liquid. Like modern almond milk, the bar-blender method would give you almond milk closer in mouth feel to cow milk than what you would attain with hand grinding the almonds.
You can use the same method to make milk from hazelnuts, walnuts, or pecans, but I do not know of any documentation for pecan milk before the American revolution.
 Master Chiquart, Du Fait du Cuisine
 I’ve never had sheep milk before.
 Almonds are drupes, not nuts.
A Boke of Gode Cookery. Almond Milk 2000. James L. Matterer. http://www.godecookery.com/goderec/grec31.htm. Accessed on November 7, 2012 , 10:12 am.
Chiquart, Maistre. Du fait de cuisine. Translated by Elizabeth Cook.
http://www.daviddfriedman.com/Medieval/Cookbooks/Du_Fait_de_Cuisine/Du_fait_de_Cuisine.html. Accessed on November 7, 2012 , 10:15 am.
Le Viandier De Taillevent: 14th Century Cookery, Based on the Vatican Library Manuscript. Authors Taillevent, James Prescott. Translated by James Prescott. Contributor Biblioteca apostolica vaticana. Edition 2, illustrated. Alfarhaugr Pub. Society, 1989.
Medieval Cookery, Almond Milk Daniel Myers, 9/15/2006.
http://medievalcookery.com/recipes/almondmilk.html. Accessed on November 7, 2012 , 9:42 am.
Scully, D. Eleanor, Scully, Terence. Early French Cookery: Sources, History, Original Recipes and Modern Adaptations. University of Michigan Press, May 7, 2002
Scully, Terence. The Art of Cookery in the Middle Ages. Woodbridge: The Boydell Press, 1995.
Scully, Terence, ed. Le Viandier de Taillevent. An Edition of all Extant Manuscripts. Ottawa: University of Ottawa Press, 1988.