Have a try with the new search box (at the top of the left-hand margin). It’s a new facility introduced by Squarespace, who host this blog.
Because this is an internal Squarespace facility, it means that the contents of the blog and the rest of the site can be indexed as soon as they are published. This means that searches are always completely up-to-date and also very fast. This simply can’t be matched by the Google search box which I was using before.