I have 1/2 gallon of milk (not raw) that turned sour in fridge (not curdled). Hate to throw it away. Can I safely use it to make cottage cheese or put into a chocolate cake?
Is half a gallon of milk that you may not need to throw out worth getting food poisoning over? If I had to choose between possible bloody diarrhea, vomiting, severe pain, seizures and possibly even death and spending a few more dollars, I certainly would spend a few more dollars.
Throw the stuff away. If it's gone sour, you have a lively colony of bacteria in there.
They may or may not be harmful, but I cannot stress enough that it's simply too dangerous to try.
Cottage Cheese, Buttermilk, Yogurt, Cheese...These are all things that are made in specific conditions, controlled in order to get a desired result.
Milk that has been in a container (that has been opened numerous times in uncontrolled environments) goes sour because of undesirable conditions and should not be confused with properly cultured dairy products. EVER.
You can cook with it in place of buttermilk. If it is NOT curdled and went sour in the fridge there is absolutely nothing wrong with making biscuits, panckes, cornbread etc with it. Honestly there's nothing to be afraid of, make sure whatever you make is cooked through completely and don't use it if it's already separated into curds and whey.