Preheat the oven to 250 degrees F (120 degrees C). Spread the bread cubes out in a single layer on rimmed baking sheets. Toast in the oven for 20 minutes, or until dry. Cool, and transfer to a large bowl.

Fry the bacon pieces in a large skillet over medium heat until crisp. Remove from the pan to drain on paper towels. Add onions to the pan with the bacon grease: cook and stir over medium heat until starting to turn deep brown, about 15 minutes.

Pour in 1/4 cup of the chicken stock, stirring to remove any bits that are stuck to the bottom of the skillet. Add the celery and mushrooms and season with sage, rosemary, salt and pepper. Drizzle this over the bread cubes, and toss to coat.

Pour the rest of the chicken broth over the bread and add the bacon, cranberries, raisins and golden raisins. The stuffing can be made up to this point up to 3 days in advance.

Preheat the oven to 350 degrees F (175 degrees C). Whisk the salt and pepper in with the eggs and stir into the bread cubes. Transfer to a disposable roasting pan, or a large baking dish. Drizzle melted butter over the top and cover with aluminum foil. If stuffing a turkey, mix in the eggs and melted butter; stuff in to the cavity right before roasting.

Bake for 30 minutes in the preheated oven, then remove the aluminum foil and continue to bake for an additional 10 to 15 minutes, until the top is browned.