I adapted it for Thermione so will give both methods.
Ingredients: (with apologies for the old fashioned imperial measurements)
3 oz margarine (I suppose butter would do too)
3 oz caster sugar
1/2 tsp vanilla extract
1 medium banana, peeled
5 oz SR flour
a pinch of salt
Whisk together the margarine, sugar, eggs, vanilla and banana. Then fold in the flour and salt.
Bake in a suitably sized loaf tin at 180C for about 40 to 45 mins - until it's done! I used a paper liner.
Or, if you are lucky enough to have a Thermomix:
Place the margarine, sugar, eggs, vanilla and banana in the bowl and puree at speed 5-6 for about 10 seconds or so, until it is a batter.
Add the flour and reverse stir at speed 2-3 until the flour in incorporated. You might need to push down the sides with the spatula.
Bake as above.
There's lots of variations: you could add chocolate or I think some crystallised, chopped ginger would go well, for example. But it's really lovely just as it comes, very easy, very simple. Also pretty frugal. I used value flour and it rose fine.
Definitely one to do again.
Edited on Sunday to say I've found the source but it's not attributal as such. If you go to Shirley Goode's blog, it is here, in the comments third comment down, from Kate, who says it was going the rounds a long time ago. http://shirleygoode.blogspot.co.uk/2013/09/keeping-in-touch.html
It's a good blog although it takes ages to read. Shirley is a character!!!