Step 3: Sour the milk
Souring milk seems counter-intuitive, i know, but you're basically creating buttermilk. It ends up lighter (and healthier) and I don't usually have buttermilk around.
Simply pour the milk into a non-reactive (i.e. glass) container and add the tablespoon of vinegar. Give it a mix and let it rest for 10 minutes. enough time to get your other ingredients together and get the oven preheated.