How much of the clove should I use when using big garlic heads?
I think that might be elephant garlic, which isn't really garlic at all. It's in the same family, but is actually a kind of leek so it has a flavor that's a cross between garlic and onion, but milder than garlic. Because it's not very strong you'll probably want to add the whole thing. Just chop it and use it as normal.