Preheat your oven to 350°F. Lining a baking sheet with parchment paper or foil will make cleanup a breeze later on!

In a small bowl, combine 1 cup panko bread crumbs and 1 cup milk. Stir well to ensure the breadcrumbs soak up all that creamy goodness.

Melt 1 tablespoon butter in a large sauté pan over medium-high heat. Add the diced yellow onion and cook until fragrant and slightly browned, about 3–5 minutes. Add in the minced garlic and cook for an additional 2–3 minutes before removing from heat.

In a large bowl, mix together the ground beef, soaked bread crumbs with milk, cooked onions, garlic, egg, Worcestershire sauce, thyme, and kosher salt. Shape this mixture into a loaf on your prepared baking sheet.

Place your meatloaf in the preheated oven and bake uncovered for about 40 minutes. While it's cooking, mix together ketchup, spicy brown mustard, and brown sugar in a bowl.

After 40 minutes, spread your sauce mixture generously over the top of the meatloaf. Return it to bake for another 30–35 minutes until it reaches an internal temperature of 160°F (70°C).