The whole point of the experiment is to show that particles -- electrons/photons/whatever -- form an interference pattern even when fired one at a time. Obviously it takes many particles to form an image of the pattern, but they are fired one at a time. That is what makes it spooky.
Agreed js1138. I'll look at the link you provided to see if they also measured and determined that only 1 electron hit the target even though only 1 was sent. Thanks