Pour the buttermilk into the saucepan.

Heat while sometimes stirring until it reaches about 120F - if you don't have a thermometer just wait until it's so hot you don't want to dip your finger into it any longer.

Turn off the heat and add one teaspoon of citric acid (or lemon juice or some rennit). Stir carefully!

Let stand for about 20 minutes.

Put a cheescloth into the collander and the collander on top of a bowl. Pour the broken apart buttermilk into the cheesecloth.

Wait about 5 to 10 minutes until most of the whey is separated, then either press the cheesecloth to remove more whey from the Quark or just put everything in the fridge. After about 2 hours or after a night, the Quark is ready to use.