In a large mixing bowl, combine the ground beef, breadcrumbs, chopped onion, minced garlic, shredded cheddar cheese, milk, egg, Worcestershire sauce, Italian herbs, salt, and pepper. Mix until just combined, taking care not to overwork the meat.
Transfer the meat mixture into a greased loaf pan, pressing it down evenly. Bake in the preheated oven for 60-70 minutes, or until the meatloaf is cooked through and reaches an internal temperature of 160°F (70°C).
While the meatloaf is baking, place the cubed potatoes in a pot of salted water. Bring to a boil and cook for 15-20 minutes or until tender. Drain well.
In the same pot, mash the potatoes with sour cream and butter until creamy. Season with salt and pepper to taste.
Once the meatloaf is done, allow it to rest for 10 minutes before slicing. Serve slices of meatloaf alongside a generous scoop of mashed potatoes. Optionally, garnish with chopped chives.