To make sour milk in place of buttermilk, combine 1 cup whole milk with 1 tablespoon vinegar (I used apple cider vinegar but you can also use white vinegar). Let the mixture stand for about 10 minutes until the milk has curdled.
Homemade Balsamic Reduction: In a small saucepan, combine 1 cup balsamic vinegar and 1 heaping tablespoon dark brown sugar. Cook down until thickened, about 20 minutes over medium-low heat.
Muffins can be stored in an airtight container in the refrigerator for up to 5 days.