In a large mixing bowl, combine ground meat, minced mushrooms, bread crumbs, onion, ketchup, eggs, and salt and pepper. Mix well. Spread 1/2 of the mixture into the bottom of a loaf pan. Arrange 6 whole mushrooms stem down into meat. Top with rest of meat, patting to combine both halves.
Bake for 1 hour and 45 minutes, or until done. Internal temperature should measure 160 degrees F (70 degrees C) when done.