For Better Meatloaf, Use This Big Little Trick

1/4 cup unsalted butter

2 large yellow onions (about 10 ounces each), finely chopped

2 English muffins

3/4 cup cold water

3 large eggs

2 tablespoons ketchup, plus more for glazing

1 tablespoon kosher salt, plus more to taste

1 teaspoon freshly ground black pepper

2 pounds ground beef (preferably 15 to 20% fat)