This is an excerpt from Alte Kochrezepte aus dem bayrischen
(Germany, ~1500 - V. Bach, trans.)
The original source can be found at
Stefan's Florilegium
To make almond porridge. Take rice, wash it well in water and dry it on a cloth. Then pound it small in a mortar and sieve it through a cloth. Make thick almond milk, put it by the fire and grind the ounded rice into it, about half a spoonful, and some sugar.