John Singer Sargent's Lady Agnew of Lochnaw is a very famous and accomplished painting, now hanging in the Scottish National Gallery in Edinburgh. In this YouTube video, American artist John Howard Sanden paints a copy of it over the course of about three hours (split over two videos) :

It is fascinating watching him do this, also a little hypnotic seeing the painting come together. He explains his thought process and what he thought Sargent did at the time he painted the original in 1892. There are many art tutorial channels and videos on YouTube and this is one of the best I've seen. As Sanden says, all the great art masters copied the great works of past masters, including Sargent. I think the final result is extremely good.

The video itself seems to be from an old tape video from the The Portrait Institute in New York. Unfortunately, it might well be an illegal upload because it starts with a warning about "duplication". So the YouTube video might disappear. In some ways this would be a shame: I had never heard of Sanden, or the Institute, but now I know what a good painter and teacher he is.

Edit: Fixed spelling on Sargent's lastname.