1. Adjust an oven rack to the middle position and heat the oven to 200
degrees. Arrange the bread on a wire rack set over a baking sheet and
bake until slightly dry, about 15 minutes.
2. While the bread is in the oven, melt 1 tablespoon of the butter and
whisk it together with the milk, egg, sugar, vanilla, cinnamon, and
salt in a medium bowl. Slowly whisk in the flour until smooth. Pour the
batter into a shallow dish large enough to hold two slices of bread.
3. Transfer 2 pieces of the bread from the oven into the batter and soak
both sides, about 30 seconds per side. Meanwhile, melt 1 more
tablespoon of the butter in a 12-inch nonstick skillet over medium heat
until beginning to brown, swirling to coat the pan. Remove the bread
from the batter, allowing excess batter to drip back into the dish, and
lay in the hot skillet. Cook until golden brown on both sides, about 2
1/2 minutes per side. Transfer the French toast to the wire rack and
keep warm in the oven. Repeat with the remaining butter, bread, and
batter.