Preheat oven to 350 degrees. Spray a 9 x 13-inch baking pan with nonstick spray; set aside.
Place bread cubes on a baking sheet in a single layer (use two sheets, if necessary).
Bake bread cubes for 10 minutes. Flip, then cook another 5 to 10 minutes, or until bread is crunchy on edges. Set aside.
While bread is cooking, melt butter in a large frying pan over medium heat.
Add celery and onions to pan; season with salt and pepper. Cook until tender, stirring occasionally (about 15 to 20 minutes).
Remove pan from heat. Stir in parsley, then adjust seasoning to taste with additional salt and pepper, if needed.
Place bread cubes in a large bowl. Top with vegetables and egg.
Add broth, a little at a time, stirring well after each addition. Add just enough broth so stuffing is moistened, but not soggy.
Transfer stuffing to baking pan. Bake for 35 to 40 minutes, or until stuffing is hot and lightly browned on top.
Serve stuffing hot. Enjoy!
Notes
Adjusting the oven temperature: if you're cooking something else at a higher temperature, it's fine to cook the stuffing at the same temp, too. Just keep an eye on the stuffing, and cook it for less time than indicated above.To prep this recipe ahead of time: cook the veggies and toast the bread, then refrigerate the veggies and store the bread in an airtight container until ready to use. On the big day, mix the veggies and bread together, along with the egg and broth. Bake according to directions above (it may take a little longer since everything is cold).