Many of the recipes from NT call for whey. I was a bit intimidated by the process at first, but now, it's like second nature to whip up a batch. Whey is useful as an inoculant and supplies lactobacilli. I use it almost daily!
Homemade whey is easy to make from good quality plain yogurt. My favorite is Seven Stars, as it is made without sugar. Sometimes I make a batch of maple flavored whey, especially when I make baked goods, but usually I just use plain yogurt. You will need a large strainer that rests over a bowl. Place 2 quarts in the strainer lined with a tea towel or unbleached cheesecloth. Cover with a plate and leave at room temperature overnight. The whey will drip out into the bowl. Place whey in clean glass jars and store in the refrigerator. The resulting matter in the strainer is a delicious cream cheese. I usually use it for making "ants on a log" or as a topping for sweet potatoes, so that the beta carotene will have the fat necessary to be able to readily convert into Vitamin A.
**Just a note from my experience: goat's milk yogurt doesn't quite produce the same amount of whey, nor does the resulting cheese get as thick!