Preheat your oven to 375°F (190°C). Grease your loaf pan lightly or line with parchment paper.
Prepare the meat mixture: In a large mixing bowl, combine breadcrumbs and milk. Allow the mixture to sit for about 5 minutes so the breadcrumbs can soak up the liquid.
Add the ground beef, eggs, chopped onion, garlic, parsley, salt, pepper, Worcestershire sauce, and mustard to the breadcrumb mixture. Mix gently until just combined.
Form the loaf: Transfer the mixture into the prepared loaf pan, pressing it in evenly but not compacting too tightly.
Make the glaze: Stir together the ketchup, brown sugar, and apple cider vinegar in a small bowl until fully blended.
Spread half of the glaze over the top of the meatloaf.
Bake for 45 minutes, then remove from the oven and apply the remaining glaze evenly.
Place the meatloaf back in the oven and continue baking for an additional 15-20 minutes, or until a thermometer inserted into the center reads 160°F (71°C).
Once baked, let the meatloaf sit undisturbed for 10 minutes before cutting into it.