See also: French Toast Recipes
Bartolomeo de Sacchi di Piadena, known as 'Platina' (15th century) wrote 'De honesta voluptate', which contained his views on food, spices, etc., discussing both culinary and medicinal uses . (Many of the recipes in the second part of his book are from an earlier work by Martino.) In this book, Platina describes a dish of bread soaked in egg batter and fried.
A recipe is also given in 'The Accomplisht Cook' by R. May (1660) for “French Toasts. Cut French Bread, and toast it in pretty thick toasts on a clean gridiron, and serve them steeped in claret, sack, or any wine, with sugar and juice of orange.”
Called 'poor knights pudding' or 'poor knights of Windsor' in England and 'pain perdu' (lost bread) in French, originally it was most likely a way to make use of crusts and stale bread.