1 slice soft sandwich bread, roughly torn into small pieces
1 cup whole milk
1 tablespoon olive oil
¼ cup onion, diced
¼ cup carrot, diced
¼ cup celery, diced
2 to 3 garlic cloves, minced
¼ teaspoon dried thyme
1 ½ teaspoons tomato paste
1 pound ground beef
1 large egg, lightly beaten
1 teaspoon Worcestershire sauce
½ teaspoon kosher salt
freshly ground black pepper
¼ scant cup ketchup, divided
2 tablespoons kewpie mayo
Preheat the oven to 350 degrees. Place the bread in a small bowl, pour in the milk, and set aside to soak until the bread is very soft and mushy.
Heat the olive oil in a large pan over medium heat. When the oil is shimmering, add the onion, carrot, and celery and cook, stirring occasionally, until the onion is translucent and the vegetables are soft, 6-8 minutes. Stir in the garlic and cook until fragrant, about 30 seconds. Stir in the thyme and tomato paste, then remove the pan from the heat and set aside to cool for about 3 minutes.
Make meatloaf mixture
In a large bowl, combine the beef, egg, Worcestershire sauce, sauteed vegetables, kosher salt, and as much black pepper as desired. Using a spoon, transfer the softened bread and add it to the bowl with the beef, discarding the milk. Using your hands, mix until just combined.
Transfer the meatloaf mixture to a foil-lined baking sheet and shape it into a loaf, about 4 inches by 6 inches.
Spread 2 tablespoons of the ketchup evenly over the top of the meatloaf.
Transfer the meatloaf to the middle rack of the oven and bake for about 45 minutes. Remove the meatloaf from the oven and spread the remaining ketchup over the top, then return the loaf to the oven. Bake until cooked through, 10-15 minutes more.
Remove the finished meatloaf from the oven ad set it aside to rest for about 10 minutes. Drizzle the kewpie mayo on top. Cut into thick, hearty slices and enjoy.