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.
Meat: You can replace the meat in this recipe with 2 pounds of "meatloaf mix", which is available at a lot of grocery stores in the meat case.
Milk: The whole milk can be replaced by ½ cup plain yogurt.
Saltines: The crushed saltines can be replaced by ⅔ cup quick oats or 1⅓ cups fresh bread crumbs.
Storage: Store leftover meatloaf in an airtight container in the refrigerator for up to 4 days.
Freeze Before Baking - Mix together the ingredients, shape the meatloaf, then wrap in plastic wrap, place in a ziploc freezer bag, and freeze for up to 4 months. Thaw overnight in the refrigerator, then bake as directed. I recommend freezing it without the glaze and making it/brushing it on right before baking.
Freeze After Baking - After the meatloaf has baked and cooled, wrap it in plastic wrap, wrap it in a layer of aluminum foil, place in a ziploc freezer bag, and freeze for up to 3 months. Thaw overnight in the refrigerator, then reheat in a 350-degree oven, covered with foil, for about 45 minutes, or until heated through. I do not recommend reheating directly from frozen, as it takes A LONG TIME and the outside can get dry while the inside remains frozen. For individual servings, slice the baked and cooled meatloaf and follow these same steps.