Preheat your oven to 350°F (175°C). Line a rimmed baking sheet with aluminum foil and lightly grease it.

Melt the butter in a small skillet over medium heat. Add the diced onion and cook for 5–6 minutes until softened and translucent. Add the garlic and cook for another 60 seconds until fragrant. Remove from heat and let cool for 5 minutes.

In a small bowl, combine the breadcrumbs and milk. Stir and let sit for 3–4 minutes to form a panade (the breadcrumbs will absorb all the milk).

In a large mixing bowl, add the ground beef, beaten eggs, soaked breadcrumb panade, cooked onion and garlic, Worcestershire sauce, smoked paprika, kosher salt, black pepper, and dried thyme.

Using your hands or a large fork, mix everything together just until combined — do not overmix. A few small streaks are fine; you want the mixture cohesive but not compressed.

Transfer the meat mixture to the prepared baking sheet. Shape it into a loaf approximately 9 inches long, 4 inches wide, and 2½ inches tall. Make sure the loaf is even so it cooks uniformly.

In a small bowl, whisk together the ketchup, brown sugar, apple cider vinegar, and Dijon mustard until smooth. Set aside.

Bake the meatloaf uncovered at 350°F for 40 minutes.

Remove from the oven and spoon or brush half the glaze evenly over the top and sides of the loaf. Return to the oven and bake for another 10 minutes.

Apply the remaining glaze and bake for a final 10–15 minutes, until the glaze is caramelized and an instant-read thermometer inserted into the thickest part reads 160°F. Total bake time is 60–65 minutes.

Remove from the oven and let the meatloaf rest for 10 minutes before slicing. This step is critical — it allows the juices to redistribute and ensures clean, cohesive slices.

Garnish with fresh parsley if desired, slice, and serve immediately.