Q: How do I create bootable Mountain Lion external HD

How do I create a bootable Mountain Lion external Hard drive, and then recover a Mountain Lion external Time Machine backup onto that bootable Mountain Lion external Hard drive, while leaving my computer's operating system and files intact.

Forget why I'm doing this, I tried to get into the reasons in a previous question and that led to much confusion as to why I need to do this and why don't I try something else instead. THIS is what I need to do, so please just answer how do this and only this.

Thank you!!