Add the chopped onion and cook until softened, about 5 minutes.
Add minced garlic and cook for another minute until fragrant.
Remove from heat and let it cool slightly.
In a small saucepan, simmer ½ cup of balsamic vinegar over medium heat until reduced to a thick syrup, about 10-15 minutes. Set aside.
In a large mixing bowl, soak the breadcrumbs in milk.
Add the ground meat, cooled onion and garlic mixture, ½ cup of balsamic vinegar (or the balsamic reduction if using), eggs, Worcestershire sauce, oregano, thyme, paprika, salt, and pepper.
Mix the ingredients gently but thoroughly, avoiding overmixing as it can make the meatloaf tough.
Transfer the mixture to a baking dish or a lined baking sheet and shape it into a loaf.
In a bowl, mix together ketchup, the remaining ½ cup of balsamic vinegar, and brown sugar.
Spread half of the glaze over the meatloaf.
Place the meatloaf in the preheated oven and bake for 45 minutes.
After 45 minutes, remove the meatloaf from the oven and spread the remaining glaze over it.
Return it to the oven and continue baking for another 15-20 minutes or until the internal temperature reaches 160°F.
Once done, let the meatloaf rest for about 10 minutes before slicing.
