Preheat oven to 425 degrees F.
Carefully cut the onions exactly in half across the equator, remove the peel, and slice the smallest 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. Remove and dig out the center of each half with a spoon to leave the last 1/4-inch around the perimeter and base. Chop them and set the removed onion bits aside for later.
In a 12 to 14-inch saute pan, heat the remaining 4 tablespoons oil over medium heat until smoking. Add the ground chuck and cook until fat has rendered and meat has started to brown, about 20 to 25 minutes.
Drain the fat, add the removed pieces of onions, and continue cooking until the onions are very soft, 10 to 12 minutes.
Remove the meat mixture from the heat and place in a bowl. Add the caciocavallo, marjoram, red wine, and 3/4 cup of the bread crumbs, stir to mix well and season with salt and pepper. Stuff each of the onion halves carefully just over the edge of each and sprinkle with remaining bread crumbs. Place onions in a well-oiled glass baking pan, drizzle with extra virgin olive oil and place in the oven. Cook until dark golden brown on top, about 20 to 25 minutes and serve.