It's so easy! An acid like white vinegar or lemon juice will curdle the non dairy milk (which is what buttermilk is - curdled milk). Simply combine the vinegar and the milk and let it sit for around 10 minutes until it looks a bit chunky/curdled. u003cbr/u003eu003cbr/u003eI like to use soy milk for dairy free buttermilk, and I find that oat milk doesn't curdle as well, and that it also depends on the brand you are using. That being said, if all you have is oat milk, I've made these using it and they were still delicious! So don't stress about which milk to use!