1. Preheat the oven to 375°F. Lightly coat a lined baking sheet with cooking spray.

2. In a large bowl, mix the ground beef, onion, breadcrumbs, ½ cup tomato sauce, eggs, Worcestershire sauce, 2 tablespoons balsamic vinegar, thyme, parsley, Parmesan, salt, and pepper until evenly combined.

3. Rinse an 8-by-4-inch loaf pan with water, then firmly pack the mixture into the damp pan.

4. Invert the pan onto the prepared baking sheet to release the loaf.

5. Bake for 50 minutes.

6. Stir together the remaining 3 tablespoons tomato sauce and 1 tablespoon balsamic vinegar.

7. After 50 minutes, brush the loaf with the glaze and return it to the oven for 20 minutes. Reserve a little glaze for a final brush after baking.

8. Melt the butter in a large skillet over medium-high heat.

9. Add the shallots and cook for 2 to 4 minutes, until softened. Stir in the garlic and cook for 1 minute.

10. Add the mushrooms and Worcestershire sauce. Cook uncovered, stirring occasionally, until browned and their moisture evaporates, about 8 minutes.

11. Sprinkle in the flour and stir to coat. Cook for 3 to 4 minutes.

12. Add the balsamic vinegar, then slowly pour in the stock while whisking to dissolve the flour.

13. Simmer, stirring often, until the gravy thickens, about 4 to 5 minutes. Season with salt and pepper.

14. Keep warm over low heat.

15. Transfer the meatloaf to a serving platter and slice.

16. Spoon the mushroom gravy over the top and garnish with parsley if desired. Serve with additional gravy at the table.