Arrange a rack in the middle of the oven and heat the oven to 200ºF. Fit a wire rack inside a rimmed baking sheet.

Cut 1 loaf white bread, challah, or brioche crosswise into ¾-inch to 1-inch-thick slices.

Place 5 large eggs, 1 ¾ cups dairy of choice, ¼ cup granulated sugar, 2 teaspoons vanilla extract, ½ teaspoon ground cinnamon, and ¼ teaspoon kosher salt in a 9x13-inch baking dish. Whisk until fully combined, no streaks of egg remain, and the sugar is dissolved.

Place as many bread slices as can fit in a single layer into the milk mixture. Soak, flipping once, until drenched but not falling apart, about 1 minute per side for white bread or about 15 seconds per side for challah and brioche. Transfer the bread slices to the wire rack; repeat soaking the remaining slices.

Melt 1 tablespoon of the unsalted butter in a large nonstick skillet over medium heat. Add as many bread slices as can fit in a single layer with space around each one. Cook until the bottoms are golden-brown and crisp, 3 to 4 minutes. Flip and cook until the second side is browned, 2 to 3 minutes more. If the bottoms are getting too dark, reduce the heat to medium-low. Transfer to a second baking sheet and keep warm in the oven.

Cook the remaining bread slices, melting 1 tablespoon of the unsalted butter in the pan before each batch. Serve with maple syrup or powdered sugar.