The bigger the better - do not peel the onions. Two ways. Wrap the onion in foil paper and place into a hot oven. It's ready when you can pierce it with a long thin sharp knife. Another way is they way they do it in C-town. Fit as many onions as you can in your baking dish, do not cover and bake. They'll blacken on top, may even smoke, before they are done inside. They'll be ready when they are soft inside. After they cool you can spoon the inside out onto bread with olive oil or simply make an onion salad with maybe some tomato, oregano, oil & vinegar.