Buttermilk substitute in baking?

[Cricket]

I've never frozen buttermilk, so can't help you on that one.
I've used low fat sour cream or plain yohurt as a substitute before with excellent results.
You can also get powdered buttermilk, I think. I've never tried it myself, but my MIL uses it. That would prevent waste - you could just reconstitute the amount you need, and the rest would keep without issues. But, like I said, I haven't tried it myself.
All the best!

[entreat]

I usually do some kind of sour cream & milk mix. Never tried the vinegar option... sounds a bit too chem-class for my liking!

[Life is Good]

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

[Traveller]

I read the title as "Breastmilk Substitute in baking" and was going to suggest using cows milk

Ahem, sorry not much help am I? As you were...

[entreat]

to get the best light & fluffy pancakes, separate the eggs, mix the yolks in as per normal, but with the white - whip them until soft peaks form, then fold them into the batter at the end. OMG... so simple, and the result is amazing! Hasn't failed me yet!