01 - Set oven to 350°F (175°C). Grease a standard 9x5 inch loaf pan with nonstick spray.
02 - In a large bowl, combine ground beef, onion, eggs, milk, panko breadcrumbs, Worcestershire sauce, salt, pepper, garlic powder, and dried thyme. Mix gently by hand until just incorporated.
03 - Transfer mixture to prepared loaf pan, pressing lightly to eliminate air pockets. Smooth the top. Bake uncovered for 55–65 minutes, until firm and an internal temperature of 160°F (71°C) is reached.
04 - Remove the meatloaf from the oven and allow to rest in the pan for 10 minutes before slicing.
05 - While meatloaf rests, melt butter in a medium saucepan over medium heat. Whisk in flour and cook for 1–2 minutes until lightly golden. Gradually add broth and tomato sauce, whisking constantly. Stir in vinegar, brown sugar, salt, and pepper. Simmer for 5–7 minutes, stirring occasionally, until gravy is smooth and slightly thickened.
06 - Slice meatloaf and arrange on a serving platter. Ladle warm tomato gravy over slices and serve immediately.