Sauté the onion, celery, carrot, scallion, bell pepper and garlic in heavy skillet for 10 minutes or until vegetables are tender and the moisture has evaporated.
Cool to room temperature and chill for 1 hour.
Mix the eggs, cumin, nutmeg, cayenne, salt and pepper in a bowl and beat until smooth.
Mix in ketchup and half and half to the egg mixture.
Add ground beef, sausage, bread crumbs and chilled sautéed vegetables.
Place the meatloaf in a baking dish and place on a large baking pan. Add boiling water to the baking pan allowing the water to reach half way up the baking dish sides.
Bake at 375 degrees for 40-60 minutes or until cooked through.
Remove baking dish from the water and let stand for 20 mintutes before serving.