One of the uses for leftover whey after making cheese is to make ricotta with it. Here is the simple process I follow for making ricotta with cheese whey.
First, after taking the curds out of the whey, I let the whey sit at room for 2 to 8 hours so that it cultures.
Next I heat the whey on high until it comes to a boil.
I then turn the heat off, cover the pot, and let it sit until it is cool. This step takes longer the more whey you are using. I just usually leave it over night and then work with it some time the next day. After sitting, the ricotta cheese will have separated from the whey and it will look like this:
Next, I strain the ricotta out through a colander lined with cheese cloth. And then I let it drain in the sink until most of the whey is out, but I let it further drain in the refrigerator overnight. Here is what the final ricotta looks like: