France, 15th c.
Recipe by Daniel Myers
Almond milk was a staple of the medieval kitchen. It was used in a wide variety of dishes as a substitute for milk or cream, especially on "fish days", when the church placed restrictions on what foods could be eaten (the most prominent of which were the days during lent). Fortunately, it is quick and easy to make.
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).
Source [Du fait de cuisine, E. Cook (trans.)]: 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....