Pour 1 litre of milk and 15ml of vinegar into a vac bag and cook in a water bath at 86°C for 90 minutes.
Pour the other litre of milk into a pan with 15ml of vinegar. Bring to the boil, then leave to rest for 30 minutes.
Line a colander with 2 layers of cheesecloth. Strain both mixes through the cheesecloth. Reserve the whey for other uses and gently combine the 2 lots of curd.