1. Preheat the oven to 350°F and set an oven rack in the middle position. Line a 13 x 18-inch baking sheet with parchment paper or heavy-duty, nonstick foil.
2. Heat the oil in a medium skillet over medium heat. Add the onion and cook, stirring frequently, until softened, about 5 minutes. Add the garlic and cook 1 minute more. Do not brown. Transfer to a large bowl.
3. To the bowl, add the milk, eggs, thyme, salt, pepper, and Worcestershire sauce. Whisk to combine.
4. Add the meatloaf mix and bread crumbs to the egg mixture and mix with your hands until just combined.

For Individual Meatloaves

1. Form the mixture into 6 small (9-ounce) loaves and place on the prepared baking sheet. Spoon the ketchup over the top and sides of each loaf. Bake for 40 to 45 minutes, or until an instant-read thermometer registers 160°F in the middle of a meatloaf. Let the meatloaves rest for about 5 minutes. Scrape any fat away from the edges of each meatloaf, then use a spatula to transfer them to a serving platter or plates.

For Family-Style Meatloaf

1. Form the meat mixture into a 12 x 5-inch loaf shape directly on the prepared baking sheet. Spread the ketchup evenly over the top and sides of the loaf. Bake for 75 to 80 minutes, or until an instant-read thermometer registers 160°F in the middle of the meatloaf. Let the meatloaf rest for about 10 minutes. Scrape any fat away from the edges of the meatloaf (it will ooze out and brown while baking), then use a wide spatula to transfer the meatloaf to a cutting board or serving platter. Slice and serve.
2. Note: Meatloaf mix is a combination of ground beef, pork, and veal that is more flavorful than ground beef alone. Most supermarkets carry meatloaf mix, but if you can’t find it, equal parts ground beef and pork is a good substitute. If you don't cook with pork, go ahead and use ground chuck, which is 20% lean ground beef.
3. Note: If making individual meatloaves, the trickiest part of this recipe is making the loaves of equal size. I usually divide the meat mixture roughly in half and then divide each half roughly into thirds. Then, I scoop large balls of the mixture onto the prepared baking sheet, reapportion if necessary, and then shape into loaves.
4. Make-Ahead/Freezer-Friendly Instructions: You can refrigerate the uncooked loaf/loaves, covered, 1 day before you plan to bake them. Allow a few extra minutes in the oven if baking from cold. For already baked meatloaf/loaves, cool completely, wrap well, and refrigerate for up to 3 days or freeze for up to 3 months. If frozen, defrost overnight in the refrigerator and then reheat, covered, on a baking sheet in a 300°F oven until hot in the middle.