Make the Glaze: In a small saucepan, whisk together the ketchup, brown sugar and vinegar; set aside.
Make the Meatloaf: Preheat oven to 350 degrees F. Heat oil in medium skillet over medium heat. Add the 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 the 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 the mixture into a 9-by-5-inch loaf shape. Place on a foil-lined rimmed baking pan (you could also use a 9x5-inch loaf pan with a perforated bottom). Brush with half of the glaze.
Bake meatloaf until it is cooked through (it should register 160 degrees F on an instant-read thermometer), about 1 hour, brushing with the remaining glaze when there is 15 minutes left. Cool at least 20 minutes, then slice the meatloaf and serve.
