Clabber can be used in place of buttermilk or even mesophilic culture for cheesemaking. I will summarize how I make it, plus here's a link to a thread about clabber from the Keeping a Family Cow forum: http://familycow.proboards.com/index.cgi?board=Food&action=display&thread=18256
If you have any questions, just let me know.
Clabber can only be made with raw milk, as pasteurized milk has all of the beneficial microorganisms killed off.
Place 1 cup of raw, skimmed milk in a sterile jar, covered with a light cloth and in a place where it will be safe. In the summer weather, my skimmed milk will clabber in about 3 days, using about 1 cup of milk for the first batch. I use about a quarter cup of that to culture the next 2 cups of milk, which takes about two days. Usually by the third generation, the clabber is very mild tasting and makes a really good culture for Neufchatel or other cheeses. Just make sure to only use a tea towel or other lightweight cloth to cover the jar or bowl that you have your clabber in. Covering with an air-tight lid will cause it to taste really bad.
If you can't bring yourself to taste the clabber, just wait until you are to the 4th or 5th generation and it should work really well for you. The clabber left after you take out your culture can be fed to chickens, pigs, dogs, or cats. They love it!
I use about 1 cup of clabber to culture 5 gallons of milk.