Homemade Buttermilk
You don’t have buttermilk, but you are desperate for homemade buttermilk pancakes or biscuits. What are you going to do? Here is a quick and easy solution!

1 Cup Whole Milk
Add one of the following ingredients:
1 ¾ Tablespoon cream of tarter;
1 Tablespoon white vinegar;
1 Tablespoon lemon juice

Add one of the above acidic ingredients to the milk and stir. Let stand at room temperature for 25 minutes. The milk should start to curdle. Stir well before using. Also, a combination of plain yogurt (¾ cup) and whole milk (¼ cup) can also be used to replace a cup of buttermilk, in most recipes.

From www.mr.breakfast.com