My mother uses (and my grandmothers used to use) sour milk in the baking of homemade bread. This was generally whole raw milk that had soured.
I'm not so lucky as to be able to get whole raw milk from a source I trust any more but occasionally a carton escapes the thirsty horde at home and goes past its expiration date. If it's only a day or so gone then I'll use it as normal given that I exercise a healthy degree of scepticism anyway about BB dates but if it's any longer then my idea would be that I'd use it in a bread recipe.
To clarify: the carton is unopened and has been refrigerated since purchase. It is not UHT milk as that's relatively rare here with HTST (72C for 15 seconds) pasteurisation the norm (probably owing to the relatively low ambient temperatures here)
The question is how long after the expiry date is it safe to use milk in this manner?