Thank you for all of your suggestions. I am making a mudcake this week and plan to use the milk / vinegar combo. Failing that I will try the frozen buttermilk option.

I like to think that I am fairly "well-versed" in the kitchen, but the buttermilk pancakes that I made a couple of months back made me feel like I should be banned from all things cooking! They were TERRIBLE - like little rubber door stops! So yeah - until I work out how to make good ones, pancakes aren't really an option