The French call French toast pain perdu — lost bread — made of dried-out slices recovered by soaking them in eggs and milk. Recipes along the same lines are mentioned as early as the fourth or fifth century in Apicius, the collection of really old recipes from Rome.
American-style French toast is kind of an abomination that’s usually made with squishy slices of brioche or challah or “white bread.” But I’m telling you: French toast is best when made with very stale bread. The drier the bread, the more liquid it can absorb without becoming mush.
It requires a little planning: If I know I am going to make French toast sometime during the week, I will cut one-and-a-half inch slices of a rustic loaf at least two to three days ahead of time. If it’s good bread — naturally leavened, high-hydration, the whole nine yards — starting with a loaf that is two or three days old is fine. (Much older than that and it can be hard to slice, even with a great bread knife.)
After I have cut the slices of bread, I let them sit out on the counter or on my breadboard. If you’re worried about pests, you can place the slices of bread in a cupboard or microwave that you’re not using. (Or a breadbox!) Walk away. Go live your life. Once a day, check the progress of your bread as it is drying out. Turn the slices over; sit them upright; allow them to have lots of air circulation.
When they’re hard and dry, they’re ready. In a bowl, thoroughly beat one egg for each slice of bread you are using. Whisk in a quarter to a half cup of milk for each egg (and each slice of bread). For a richer version, use half cream and half milk, or all half & half. Add a small pinch of salt. If you like sweeter French toast, add a little sugar or a drizzle of honey and perhaps a splash of vanilla extract or orange-blossom water.
Lay the dried bread in a shallow, non-reactive baking dish in a single layer. Ideally, you want to use a dish sized to just fit the amount of bread you are using: too much extra space and the bread won’t absorb as much of the eggs and milk.
Pour the egg and milk mixture over the bread. The bread won’t be completely submerged; that’s fine. Turn the…