I was making a bran muffin recipe that called for 3/4 c buttermilk, which I didn't have. I took 3/4 c fat-free milk and added 2 tsp white vinegar and let it sit. I added 1 tsp vanilla.
Since I was going to use coconut oil in the recipe and thus needed the "buttermilk" to be slightly warmer than room temperature (so the oil wouldn't harden), I put the "buttermilk" in the microwave for 30 seconds. The photo shows the unwanted result - I guess the milk separated from the whey and formed this glob. Can I assume this is unusable? I'd like to understand better what happened.