Buttermilk. It's one ingredient I always forget to purchase and can't make great biscuits without.
Years ago I had a friend who was addicted to it, she couldn't get enough, I would say she may drank a half a gallon a day - I thought she was crazy. I did not yet realize the love I would find in buttermilk many, many years later.
So, here I am just about to make a huge batch of biscuits and I find myself cursing the aging process because yet again, I have forgotten to purchase it again. I have now decided to make my own from now on.
The best way to begin this process is to have a "cultured buttermilk" starter. Much like the sour dough starter that you may read so much about, it's the best way to get the proper buttermilk one would need to bake, drink and cook with. Start with the store bought stuff and make certain it says "cultured" on the label, this will be your starter. Simply mix 1 part starter with 3 parts milk (any percentage of fat will do), pour in a glass jar or bottle, sit in a warm place in your kitchen for 24 hours and DONE! Put the finished product in the fridge and it keeps for weeks! Love it!
Here is a great place to read up on the details:
http://biology.clc.uc.edu/fankhauser/cheese/buttermilk.htm
Good baking!