Preheat the oven to 375 degrees. Put water on the stove to boil, add bullion once the water is boiling and take off heat. Saute the onion, on low heat, in the oil from the sun-dried tomatoes until onions are clear, about 8 minutes.

In a large bowl, mix the ground beef, tomatoes, sautéed onions, egg, garlic, breadcrumbs and half of the sliced mushrooms (save the other half for the gravy). Freeform the meat into a loaf in a roasting pan, then pour beef stock into the bottom of the pan. Cook meatloaf for 1.5 hours, basting regularly.

Once meat is cooked, remove from oven and let sit for 15 minutes. Move meatloaf to a platter and put the roasting pan on the stove over medium, high heat. Mix two tablespoons of flour with water, then whisk into juices in the roasting pan. Add mushrooms and stir until the liquid starts to simmer. Once simmering, add milk and stir until you have a rich gravy for your meatloaf!