Preheat your oven to 400 degrees Fahrenheit. Lightly grease a standard 12-cup muffin tin.
In a large bowl, combine the breadcrumbs and milk; let stand for 5 minutes to soften.
Add the ground beef, beaten egg, chopped onion, minced garlic, salt, pepper, Worcestershire sauce, and 1/4 cup ketchup to the breadcrumb mixture.
Mix gently with your hands until just combined. Do not overmix.
Divide the meat mixture evenly among the 12 muffin cups, pressing lightly to form a compact shape.
In a small bowl, whisk together the maple syrup, Dijon mustard, and apple cider vinegar for the glaze.
Brush about half of the glaze mixture evenly over the tops of the meatloaves.
Place the muffin tin in the preheated oven and bake for 15 minutes.
While the meatloaves bake, toss the chopped root vegetables with olive oil, salt, pepper, and thyme on a small baking sheet.
After 15 minutes of meatloaf baking, remove the tin from the oven. Brush the remaining glaze over the tops.
Return the meatloaves to the oven. Place the sheet pan of vegetables on a separate rack in the oven.
Bake for an additional 10 to 15 minutes, or until the internal temperature of the meatloaf reaches 160 degrees Fahrenheit and the vegetables are tender.
Let the meatloaf muffins rest in the tin for 5 minutes before carefully removing them. Serve immediately with the roasted vegetables.
Notes
You can prepare the meat mixture and place it in the muffin tin up to 24 hours ahead. Cover and refrigerate. Add 5 minutes to the initial baking time if cooking cold.
These individual meatloaves freeze well. Cool completely, then place them in an airtight container separated by parchment paper. Thaw overnight in the refrigerator before reheating.
Substitute the root vegetables with broccoli florets or green beans for a faster cooking side dish.