Preheat oven to 425 degrees F.
Carefully cut the onions exactly in half across the equator, remove the peel and slice a small amount from the point end, so that the halves will stand upright on the point end. Place the halves upright on a cookie sheet, season with salt and pepper, and drizzle with 4 tablespoons oil. Bake until just softened, about 15 minutes.
In a 12 to 14-inch saute pan, heat the ground beef over high heat and cook until browning in its own fat. Remove to a bowl and add the caciocavallo, marjoram, red wine, and 3/4 cup of the breadcrumbs. Stir to mix well and season with salt and pepper.
Stuff each of the onion halves carefully with the mixture, to just over the edge, and sprinkle with the remaining breadcrumbs. Place the onions in a well-oiled glass brownie pan, drizzle with extra-virgin olive oil and place in the oven. Cook 20 to 25 minutes, until dark golden brown on top, and serve.
Recipe copyright 2000, Mario Batali. All Rights Reserved.