Cut a 12 centimetre circle in the top of the cob loaf, then use a small serrated knife to cut down to 1 centimetre from the bottom. Remove this piece of bread from the middle, trying to keep most of it in one piece. Put this piece to the side.
Cut another circle around the hole in the loaf, leaving a 2 centimetre ‘wall’. Stuff three-quarters of the cheese into this wall cavity, taking care not to damage the wall. Use a spoon or palette knife to spread one half of the butter inside the main hole, then place onto a flat baking tray and brush the outsides with the melted butter. Bake for 20 minutes, until the cheese is fully melted.
While the loaf is baking, heat a flat griddle pan. Cut two 2-centimetre slices from the top of the reserved middle of bread. When the griddle is hot, lay the bread slices on and pile with the remaining cheese. Take care not to let the bread burn and wait for the cheese to melt, then flip one on top of the other to create a sandwich. Spread butter on the top and flip it over to cook, using a spatula to press it down, until nicely browned. Then butter the top and flip to cook the remaining side, then put to one side or into a low oven to keep warm.
Heat the tomato soup in a saucepan. Once the cheese in the loaf is fully melted, remove from the oven and put into a large serving dish. Pour the hot tomato soup inside, and top with the grilled cheese ‘hat’. Serve immediately.