In the good old days, the bread was kept in a bread box until it was either eaten or had become stale and ready to be discarded. This was called ‘lost bread’ or in French, 'pain perdu'.
So here is what we did to save the bread.
Depending on ones preferred taste, we would beat 2-3 eggs, add a pinch of cinnamon, and a generous teaspoon of sugar. Then we would add a splash of milk to fill our container of mix to ¾ to 1 litre, depending on the number of slices you wanted to save.
In a pie plate, we would put one slice of bread at a time and pour the mixture onto the slice so that it would absorb the mixture. When it became nicely soaked, we would pick it up, let it drain off the excess, and fry it with butter in a frying pan on medium low until golden brown. Then turn it over and fry the other side.
So the delicious pain perdu (lost bread) were eaten covered with butter and sugar to taste.
I’m from Belgium and I still cant figure why you call this ‘French’ toast. Is this from Quebec?
P.S. - Still have leftover liquid? Add some flour to obtain the right consistency and make some very nice crepes! By flambéing them 'au rum' , you are making very delicious "crêpes Suzettes"!