Coat a 2-1/2-quart shallow baking dish with nonstick cooking spray. Toss apple slices with flour in a small bowl.
Cut loaf of bread in half diagonally (to form triangle-shaped slices). Layer half the bread and half the apple slices, overlapping, in bottom of prepared dish.
In medium-size bowl, whisk together eggs, milk, 1/2 cup caramel, 1/3 cup sugar and salt. Pour half over bread and apples in dish. Repeat layering, using all remaining bread and apples. Pour second half of egg mixture over layers. Cover dish with plastic wrap; press lightly. Refrigerate to soak 30 minutes to 1 hour.
Heat oven to 375°F. Unwrap dish; sprinkle with remaining 2 tablespoons sugar. Bake at 375°F for 30 minutes; cover with foil and bake 15 more minutes or until center measures 160°F on an instant-read thermometer. Drizzle top with additional caramel sauce; let cool on rack 15 minutes. Serve warm with ice cream, if desired.