[WG.]

I've just made some and it is bl**dy lovely ...

home-made yogurt (whole milk)
bottled blackcurrants (low sugar)

Blended together until super-smooth.  I didn't grow the blackcurrants myself but got them on a barter deal in the summer.  I bottled them with only 3oz sugar to a 600ml jar.  Along with the yogurt, this gives a wonderfully sharp flavour to the smoothy.

Also make strawberry but that isn't quite so sharp (2oz sugar to 600ml).