In a liquid measuring cup, combine the milk and lemon juice or distilled white vinegar.
Stir together and let sit for 5 to 10 minutes. Use immediately.
Video
Notes
For a richer, thicker buttermilk, use half and half instead of whole milk. This is a great option if using the buttermilk for a frying dredge or salad dressings. I recommend sticking with whole milk if using it in baking recipes.
You can use a variety of different acids. If you don’t have white vinegar or lemon juice, you can use another neutral-flavored vinegar, like apple cider vinegar or lime juice.