Preheat the oven to 350 degrees. Line a rimmed baking sheet or 13-by-9-inch shallow baking dish with foil. 

Place the bread and milk in a large bowl, making sure the bread is soaking up all the milk.

Heat the olive oil in a large skillet over medium heat. Add the onion, celery, parsley, garlic, 1 teaspoon salt, and ½ teaspoon pepper. Cook, stirring occasionally, until the vegetables are soft, 5 to 7 minutes. Remove from the heat and stir in the Worcestershire. Break the bread up with your fingertips so that there are no clumps, then add the vegetables to the milk-soaked bread. Add the beef, pork, eggs, ¼ cup ketchup, 1 ½ teaspoons salt, and 1 teaspoon pepper. Use your fingers to mix everything together, being careful not to mash it.

Transfer the mixture to the prepared baking sheet and form a long loaf that is approximately 5 inches wide. Brush the top with ¼ cup ketchup. Bake for 60 to 75 minutes, or until an instant-read thermometer registers 155 degrees. Let the meatloaf rest for 15 minutes before slicing. Sprinkle with parsley and serve with ketchup on the side.