Preheat the oven to 350F. Line a large baking tray with foil. Cut a channel along the length of the top of the loaf and remove the bread from it. Scoop out the majority of the bread from the inside of the channel, but leave enough bread along the bottom and around the sides for stability. Place the hollowed out loaf on the baking tray and set it aside.
Before starting, you want to drain the spinach and the artichokes of their extra moisture really well, that way your dip doesn't turn watery. Place the spinach in a fine mesh sieve and press down on it to drain some of the excess water. Then take handfuls of the spinach and squeeze out as much extra water from it as you can. Use your hands to also gently squeeze the excess water from the artichoke hearts.
Place the drained spinach and garlic into a food processor and pulse a few times to mince it all up. Add the artichoke hearts and process until everything is chopped small and combined.
Add the cream cheese, mayo, sour cream, parmesan, white cheddar, 1/2 cup of the mozzarella, the salt and pepper to the food processor and let it run until everything is thoroughly combined. Stop to scrape down the sides with a rubber spatula as needed. If using the bacon, then add it in now and pulse a few times to incorporate it in.
Spoon the dip into the bread, pressing it down as you go to get it completely filled. Depending on the size of your loaf, you might have some dip leftover, but you can either bake it separately or you can freeze it for another time.
Bake the loaf for 15 minutes. Then remove it from the oven and sprinkle the remaining mozzarella cheese over the top. Return it to the oven and bake an additional 15 minutes or until everything is hot and the cheese over the top has melted and started to turn golden.
Let it cool for a few minutes, then use a large, serrated knife to slice it in a gentle sawing motion and serve.
