Preheat oven to 350°F (175°C). Lightly grease a 9x5-inch loaf pan or line a baking sheet with parchment paper.
Prepare vegetables by dicing the onion finely and mincing the garlic. Sauté in a small pan with a bit of oil until softened, about 3-4 minutes. Let cool.
Mix wet ingredients in a large bowl. Combine the beaten egg, milk, and Worcestershire sauce.
Combine dry ingredients by adding breadcrumbs, salt, pepper, and thyme to the wet mixture.
Add meat and vegetables to the bowl. Add the ground beef and cooled onion-garlic mixture. Mix gently with clean hands until just combined - don't overmix.
Shape the meatloaf by transferring the mixture to your prepared pan or forming into a loaf shape on the baking sheet.
Prepare glaze by whisking together ketchup, brown sugar, vinegar, and Dijon mustard in a small bowl.
Apply initial glaze by brushing half of the glaze over the top of the meatloaf.
Bake for 45 minutes, then brush with remaining glaze and continue baking for 15-20 minutes until internal temperature reaches 160°F (71°C).
Rest and serve by letting the meatloaf rest for 10 minutes before slicing. This helps it hold its shape and redistributes juices.
