Why this recipe works:
When it comes to French toast, the results are rarely worth the trouble. The bread is soggy, too eggy, or just plain bland. We wanted to come up with French toast that’s crisp on the outside and soft and puffy on the inside, with rich, custard-like flavor every time.
We first focused on determining which type of bread fared best in a typical batter made with milk and eggs. Tasters eliminated French and Italian breads for being chewy. We then turned to white sandwich bread, which comes in two kinds: regular and hearty. Regular bread was gloppy both inside and out. Hearty bread crisped up nicely on the outside, but still had mushiness.
Drying out the bread in a low oven, however, produced French toast that was crisp on the outside and velvety on the inside.
As for flavor, tasters thought the French toast tasted overly eggy. We recalled a recipe that required bread dipped in milk mixed with just yolks, versus whole eggs. The yolks-only soaking liquid made a huge difference, turning the taste rich and custard-like. Research revealed that most of the flavor in eggs comes not from the yolk but from the sulfur compounds in the whites, so problem solved.
For flavorings, we settled on cinnamon, vanilla, and brown sugar. For nutty butter flavor, we incorporated melted butter into the soaking liquid, warming the milk first to prevent the butter from solidifying. A final bonus—the recipe works just as well with challah (pronounced "hallah").