To make the meatloaf: Preheat the oven to 350 degrees F.
Place the bread in a small dish, cover with milk, and set aside to soak. Meanwhile, in large bowl, mix the beef, onion, celery, ketchup, egg, Worcestershire sauce, barbecue sauce, garlic, basil, mustard, salt, pepper, and crumbled bacon.
Squeeze excess milk from the bread, then use your hands to squeeze the bread into the meat mixture until fully incorporated. Transfer the mixture to a ring mold pan and top with the sliced, uncooked bacon. Place the ring mold on a baking sheet and bake until meatloaf is cooked through, about 45 minutes.
Meanwhile, to make the mashed potatoes, cook the potatoes, covered, in boiling salted water until tender, about 12 minutes. Drain and mash the potatoes or pass them through a ricer. Stir in the heavy cream, butter, sour cream, chives, and horseradish, if using. Season with salt and pepper, to taste. If desired, put 1 cup of the potatoes in a pastry bag fitted with a large star tip. Set aside.
When the meatloaf is done, turn on the broiler. Remove and discard the bacon slices and carefully pour the pan juices into a saute pan. Invert the ring mold onto an ovenproof platter. Using a spatula, cover the meatloaf on all sides with mashed potatoes, as if frosting a cake. If using a pastry bag, add decorative swirls to the top. Place the platter under the broiler until potatoes are nicely browned, about 10 minutes.
Meanwhile, to make the gravy, place the saute pan with drippings over medium heat and stir in the flour. Cook, stirring constantly, for 2 minutes. Stir in the broth, ketchup, mustard, Worcestershire sauce, and barbecue sauce.
If desired, fill the center of the meatloaf with buttered carrots and peas. Slice the meatloaf, and spoon the gravy over the top. Serve immediately.