One day before place the cubes of dry bread in a large bowl and leave the bread out, covered with a paper towel, to let it dry.
Set the EGG for indirect cooking with a convEGGtor at 350°F/177°C; add the cast iron skillet to preheat.
Add 2 tablespoons of the butter in Big Green Egg cast iron skillet. Cook the celery and onion until translucent, but not brown. Remove from the EGG and pour the cooked celery and onion into the bowl with the bread. Add all of the herbs and 2 cups of the chicken broth to the bread mixture. Mix well to combine.
In another small bowl, add the remaining cup of broth and the egg. Whisk lightly to combine. Pour the egg mixture over the bread and mix well. Put the mixture into the cast iron skillet and bake for about 1 hour until lightly browned on top. Right before you serve the stuffing, dice the remaining butter and add it to the top to melt. Garnish with fresh thyme and rosemary leaves. Enjoy!