To prepare the French toast, combine eggs, milk, vanilla, cinnamon, and salt in a shallow bowl; whisk until well combined. Lay challah slices in egg mixture to coat, turning slices occasionally to allow bread to absorb all of the liquid.

For the filling, place a 10-inch oven-safe skillet over medium heat. Add butter and brown sugar and cook for 2 to 3 minutes, until lightly golden and caramelized. Remove from heat. Sprinkle in the cranberries, pecans, and cinnamon. Gently press apple halves into the caramel so they are "standing" and line up one behind another so there is a flat surface on top (you may need to cut some of the halves to fill in the gaps).

Preheat oven to 350 degrees F. Place the soaked slices of challah over apples so they are completely covered. Bake in the middle of the oven for 55 to 60 minutes, until the top is golden and puffy and the apples are knife-tender. Cool slightly. Place a large platter over the top of the skillet. Being very careful, turn the skillet and the platter together, so the skillet is on top and the whole French toast dish comes out on the platter. Remove the skillet. Serve warm.