All you need is whipping cream and a mason jar.
Fill the jar less than half full (you need some sloshing around room)
SHAKE AND SHAKE AND SHAKE!
At first you will make whipped cream.
It's soundless as you shake.
Keep shaking (maybe 7 minutes in total - kids are GREAT for this).
You will know you are done when the jar starts making sloshing sounds. A lump of butter will have separated from the milk.
Pour off the liquid and save it. That's buttermilk.
Squeeze the butter with a spoon (or cheesecloth) to get all the liquid out.
Rinse your hunk of butter with plain water and press it once more. No salt, no color, no preservatives (so keep it in the fridge, not on the counter).