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 slices of bread over to completely coat. Cover the dish (plastic wrap will do), and place in the refrigerator for eight to twelve hours or overnight, flipping the bread over at least once after a few hours. You want the bread to absorb as much of the milk and eggs as possible. It should get very soft without falling apart.
Heat a skillet (or griddle) large enough to allow the slices of bread full contact with the bottom of the pan. When the pan is hot, toss in a knob of butter and allow it melt. When the foaming subsides, carefully place a slice or two of bread in the pan (don’t crowd: you may have to cook in batches) and turn the heat down to medium. Pour any leftover milk and egg mixture over the top of the bread, being careful not to spill any into the pan itself.
After a few minutes, lift a corner of a slice and check on the progress. I like golden brown, but not particularly dark — overcooked eggs taste terrible. If the color is where it should be, flip the bread over and brown the other side; watch the heat and lower it as necessary. You want the surfaces of the French toast to be nicely browned and the interior just cooked.
Assuming you’re using an ovenproof skillet, you can alternatively put the pan into a 375-degree oven immediately after you flip the slices.
Serve as is or top with more butter, warm honey or jam, dark maple syrup — or any way you see fit. You’ll never go back to mush.