I didn't necessarily love everything Dame Maggie appeared in. (I loathed Downton Abbey; sorry, but I did.) However, she was usually one of the best things in any production.
In the following, she is the only thing in the production. Aside from the crew, the director, and the writing of Alan Bennett. Other actors have played this role, and beautifully, but this is definitive. As she was.
If you have the fifty minutes, treat yourself.