Preheat your oven to 300 degrees F.
Cut the challah bread into 1 inch cubes. Place them on a sheet pan with the chopped pecans and toast them in the oven for 12 to 15 minutes, giving them a toss halfway through.
While the bread and pecans are in the oven, cut and prepare the rest of the vegetables.
Once the bread is lightly golden brown and toasted, remove the sheet pan from the oven and increase the temperature to 350 degrees F.
Heat a drizzle of olive oil in a large skillet over medium heat. Add the chopped onions and a pinch of salt. Cook for about a minute, then add the leeks, celery, and apples. Stir to combine it all and cook until it all softens.
Prepare a large baking dish by spraying it with nonstick spray. (Mine was 11 inches by 13 inches, but you can use two smaller baking dishes if you don’t have one large one.)
To create layers, add half of the bread, pecans, and squash to the dish. Top with half of the dried cranberries and cooked vegetables. Sprinkle with half of the chopped fresh herbs and another pinch of salt. Continue that process again until everything is placed in the dish.
Beat the eggs and pour them over everything, along with the chicken broth and turkey drippings. Give the baking dish a slight shake to coat all the bread and squash in the juices.
Cover the dish with foil and bake in the oven for 25 to 30 minutes.
Remove the foil and increase the oven temperature to 400 degrees F. Bake for another 25-30 minutes, until the top pieces of bread turn beautifully golden brown.