This is an excerpt from The Neapolitan recipe collection
(Italy, 15th c - T. Scully, trans.)
The original source can be found at
University of Michigan Digital General Collection
White Sauce. Get almonds for the amount [of sauce] you wish to make, blanch them and grind them as much as you can; get a crustless loaf of white bread soaked in verjuice and pound it with sugar and white ginger, and distemper it with verjuice or lemon juice or orange juice; make it quite white.
[Note that any sauce should be rather thick.]
Recipes with similar titles:
179 A white sauce (Das Kuchbuch der Sabina Welserin)
White sauce (Le Recueil de Riom)
15 WHITE SAUCE (Libre del Coch)