Like a Sourdough Cowboy making your own isn't that hard

I find myself humming “Like a Rhinestone Cowboy” — immortal lyrics from the recently passed Glenn Campbell, when I get random requests from people looking for sourdough starter. (No, that’s not what he was singing about in his amazing song that I used to sing for the nuns in Caherdavin, aged 4, and no doubt turning my foot cutely inwards as I did so.)
What am I on about? Sourdough, yes I’m the sourdough cowboy, because it’s September and that means Sourdough September. Who needs Movember when you can have amazing home-baked bread instead? The starter, ah it is shrouded in mystery. “Where did you get yours?” “Will you give me some?”