I found these recipes digging around the files at the extension office. Who says volunteer work doesn’t pay off. The date on this publication was 1977 which is the same year my husband was born. They were definitely targeting the back-to-the-land types with these.
1 quart skim milk
1/2 cup commercial buttermilk
Stir these together well and let them sit at room temperature until the mixture thickens. Once the mixture is thickened it can be chilled. If you save back 1/2 cup of this buttermilk for your next batch, making buttermilk is probably more economical than buying it at the store, especially if you use it for this next recipe, as well.
2 cups whipping cream
2 tablespoons buttermilk
Pour the cream and the buttermilk together in a mason jar and shake vigorously. Let it sit in a warm spot for 24-48 hours until the cream thickens. (Try sitting the jar on your water heater. It works for making infused oils. I don’t see why it wouldn’t work for this process.) Chill the mixture overnight and use like you would sour cream.
I used my immersion blender to cream it up a bit. This is not a necessary step but it will look more like the sour cream you buy at the store, if you do this.