It's important that the milk is raw or pasteurised in low temperature - cause high temperature (especially UHT) kills the bacteria that turn milk into sour milk. If milk was pasteurised in too high temperature, the sour milk will have bitter taste and quark will be to bitter to eat.

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- raw milk, or (if not available) good pasteurised milk from shop

1. Leave the milk in room temperature for 1-3 days, until it gets thicker and turns into sour milk. The longer the time, the more sour the quark will be. Taste it to measure how much sour it is and to check if there is any bitterness.
2. Pour the sour milk to a pot and heat it on low temperature. Be careful not to boil it!
3. After few hours all the milk will curdle into quark. Pour it through a strainer with small holes to separate bits of quark from whey.