Step 1

Preheat the oven to 350°F.

Step 2

Beat 1 egg in a large bowl. Finely chop until you have 1/4 cup minced onions, then add to the bowl. Add 1 1/2 pounds ground beef, 1 cup breadcrumbs, 1 1/4 cups whole milk, 1 tablespoon Worcestershire sauce, 1 1/4 teaspoons kosher salt, 1/4 teaspoon ground black pepper, 1/4 teaspoon celery salt, 1/4 teaspoon garlic salt, and 1/4 teaspoon dry mustard. Stir with a fork until combined. Transfer to an ungreased 9x5-inch loaf pan and pat into an even layer.

Step 3

Place 1/2 cup ketchup, 2 tablespoons packed light brown sugar, and 2 teaspoons yellow mustard in a small bowl and stir to combine. Spread evenly over the meatloaf.

Step 4

Bake until the center of the meatloaf registers 160ºF, 1 to 1 1/2 hours. Let cool for 10 minutes before slicing and serving.