In a large heavy-bottomed skillet set over medium-low heat, cook the bacon, stirring occasionally, until it crisps, 8 to 10 minutes.
Stir in the carrots, celery, onion, and garlic and cook, stirring occasionally, until softened and lightly browned, 7 to 8 minutes.
Stir in the ketchup, reduce the heat to low, and cook until the vegetables are completely tender, 10 to 15 minutes more. Transfer to a bowl and let the vegetables cool completely.
Preheat the oven to 350°F (180°C).
In a large bowl, combine the beef, pork, and bread crumbs.
In another large bowl, whisk together the milk, eggs, and salt until smooth. Pour over the meat. Add the cooled vegetables and use your hands or a rubber spatula to mix everything together.
Gently press the meatloaf into a 9-by-5-by-3-inch (23-by-13-by-8-cm) loaf pan.