Spread the cubed white and wheat bread evenly across two large baking sheets. Bake at 275°F (135°C) for 40-45 minutes until completely dried out and lightly crisp. Set aside to cool.

Melt the unsalted butter in a large sauté pan over medium heat. Add the diced celery and onions, cooking slowly for 8-10 minutes until you have softened pale green celery and completely translucent diced onions.

Transfer the toasted bread cubes to a large mixing bowl. Add the warm butter and vegetable mixture, half of the chopped fresh parsley, fine black pepper, and coarse salt. Toss gently to combine.

In a separate bowl, vigorously whisk the eggs into the chicken or turkey broth. Slowly drizzle this mixture over the bread, folding carefully until evenly absorbed to create moist centers.

Transfer the mixture to a 9x13-inch white ceramic baking dish, spreading into an even layer. Bake uncovered at 375°F (190°C) for 35-40 minutes until golden brown, crispy edges form on top.

Remove from the oven and immediately sprinkle with the remaining fine black pepper, coarse salt, and chopped fresh parsley. Artfully arrange the whole fresh sage leaves across the top before serving.