Glaze: In a small saucepan, whisk together the ketchup, brown sugar and vinegar; set aside. Preheat oven to 350F. Heat oil in medium skillet over medium heat. Add onion and garlic and sauté until softened, about 5 minutes. Set aside to cool while preparing the remaining ingredients.

In a large bowl, whisk together eggs, thyme, salt, pepper, mustard, Worcestershire sauce, cayenne, and milk. Add the ground meats, crackers, parsley, and cooked onion mixture; mix with a fork until evenly blended.

With wet hands, pat mixture into a 9x5 loaf shape. Place on a foil-lined rimmed baking pan or use a 9x5 loaf pan. Brush with half of the glaze. Bake loaf until it is cooked through (160 F on an instant-read thermometer), about 1 hour. Cool at least 20 minutes. Simmer remaining glaze over medium heat until thickened slightly. Slice the meatloaf and serve with extra glaze and mashed potatoes.