Preheat the oven to 350 degrees F (175 degrees C).
In a food processor or blender, combine the bell pepper, onion and celery. Process until finely chopped, but not liquid. Transfer to a large bowl. Add the ground beef, ground pork, cracker crumbs, onion soup mix, salt, pepper, sage and milk. Mix well using your hands, or if you have a stand mixer, mix using the paddle attachment. Transfer to a 9x5 inch loaf pan and form into a loaf, mounding in the center. Cover with a generous layer of ketchup.
Bake for 1 1/2 hours in the preheated oven. Serve hot. Refrigerate leftovers, slice and serve cold in sandwiches.
