Add cream to a pint sized (or larger) jar.

Spoon sour cream and mix thoroughly.

Secure jar lid and shake gently for 1-2 minutes until cream thickens. Stop before it "breaks", otherwise you'll end up making butter and buttermilk!

Burp lid, then let it ferment at room temperature (ideally 75°F/24°C) about 24 hours.

Stir contents and taste. If it needs more souring, let it ferment another day or two.

Store in refrigerator with lid on.