1 loaf challah or brioche (1 pound), cut into about twelve ¾-inch-thick slices
5 tablespoons unsalted butter
1 cup plus 2 tablespoons packed light-brown sugar, divided
Kosher salt (we use Diamond Crystal)
1 tablespoon fresh lemon juice
4 crisp apples, such as Gala, Braeburn, or Envy, peeled and cut into 1-inch wedges (about 5 ½ cups)
6 large eggs, whisked
1 ⅓ cups whole or 2 percent milk
2 teaspoons pure vanilla extract
½ teaspoon ground cinnamon
Confectioners' sugar
Greek yogurt, toasted chopped pecans, and raspberries or pomegranate arils, for serving
Spread bread slices on a baking sheet; let stand at least a few hours and up to overnight.
Melt butter in a large ovenproof, nonreactive skillet (like an 11-to-12-inch enameled cast iron) over medium heat. Add 1 cup brown sugar, 1/4 teaspoon salt, and lemon juice. Cook, stirring, until sugar dissolves, then bring to a boil; cook 1 minute.
Add apples and cook, turning occasionally, until they begin to soften and brown a bit and liquid thickens, about 12 minutes. Let cool 30 minutes.
In a wide, shallow dish, whisk together eggs, milk, remaining 2 tablespoons brown sugar, vanilla, and 1/4 teaspoon salt.
Dip bread in mixture, turning to coat. Arrange atop apples, shingling in concentric circles. Pour remaining mixture on top. Cover; refrigerate at least 2 hours and up to 24.
Preheat oven to 350°F. Sprinkle French toast with cinnamon and bake, uncovered, until set and golden on top, 35 to 45 minutes.
Let stand 15 minutes. Dust with confectioners' sugar; serve with yogurt, pecans, and fruit.