Liss, your 'homemade buttermilk' recipe is not actually buttermilk, but sour milk (no longer sold in stores today). Although they are easily interchangeable for baked goods, for non-baked goods, sour milk and buttermilk aren't necessarily equivalent as buttermilk (what is left after butter making) does not have a sour flavor. 'Cultured' buttermilk, on the other hand, does have a mildly sour flavor.

Here's what my Aunt does. I have never actually tried this--she happened to be here right after I read this post.

Buttermilk (this is cultured version): Take 1/4 cup of buttermilk and add four cups of milk to a mason jar.

Cover and shake a little, then put on the counter.

In about 24 hours, I have buttermilk. I just have to remember to save a little buttermilk from each batch for the next batch.

Sour cream:

same as above recipe, only you use heavy cream in place of the milk.

Keep refrigerated once the process is complete.