Weigh or portion out the bread. Cut the bread into 1-inch cubes and place on a sheet pan. Toast the bread cubes at 250 F (120 C) for an hour to achieve crunchy toast cubes.
Add a stick of butter to a medium pan over medium heat. When the butter is melty and starting to bubble, add celery and onions and cook for about five minutes until the vegetables start to soften.
Once the celery and onions are soft, add garlic and cook for 1 minute. Then add rosemary, thyme, sage, parsley, salt, and black pepper. Cook for an additional 1 minute and then remove the pan from the heat. Stir to combine everything very well.
In a large bowl add the toasted bread cubes. Once the celery and onion mixture is cooled off add it to the bowl with the toasted cubes and toss everything together.
Wisk your egg in a small bowl and add to the large bowl with everything else (except for the broth).
Stir to combine everything well then add the broth and mix to get everything soggy and moistened by the broth.
Butter a 9 x 13-inch baking dish.
Add everything to the baking dish. Do not smash everything together, keep things loosely packed. Right before you put it in the oven use a fork and sort of fluff the top so that you'll have some craggly bits on top which will brown and crisp up.
Bake at 350 F (175 C) covered with aluminum foil for 45 minutes and then uncover for an additional 15 or 25 minutes to darken and crisp the top.
Serve while warm.