You don't really need to 'prune' basil. If you harvest it regularly for eating that should be sufficient. You could certainly take the top off that stem and use it in the kitchen. It will quickly throw out two stems from the leaf axils below the cut. 1 or 2 would work, it isn't crucial where exactly you snip.

Thanks,

But I am a bit confused as to where the new stems would grow in...to me it seems like there is already a stem above every single leaf, are these not true stems?

Your plant doesn't have a finite number of stems. It can keep growing more until the end of the growing season. In the angle between every leaf petiole and the stem it is attached to there is an axillary bud. Every one of those buds has the potential to grow into a new stem. This is how the process of 'bushing' out works. Just snip off your basil at 1 or 2 and you will see what happens.

Yes, you're right, I should see for myself.
I just went out and cut it, thanks.

Every stem you cut will grow back two stems.

I have one other question, if I was to pluck a single leaf off the main stem, would a new one grow back in the same place?

After I cut off the top I picked a single leaf which looked badly damaged by leafminers. But I left the petiole-will a new one grow in its place or should I just remove the entire thing? Not that it really matters but it looks stupid just sitting there with no leaf on it.

No, a new one won't grow, but you get a new stem growing there as explained before.

The petiole will shrivel and die. But a new shoot may grow from the leaf axil. Whether it does or not is down to circumstances - water, nutrition, what's going on elsewhere on the plant, but the potential to grow a shoot exists at every axil.