Preheat the oven to its lowest setting. Put all the milk in a saucepan and heat to 30°C (86°F). Gently stir in the rennet and salt. Pour into four 100 ml (3½ fl oz) plastic dariole moulds, filling them three-quarters full. Cook in a 36°C (97°F) water bath in the oven for 4 hours (use a temperature probe to ensure the temperature stays constant). Cool in the moulds to room temperature, then chill in the fridge (still in the moulds).
Line a perforated tray with a clean cloth and sit it on another tray. Turn out the chilled milks onto the cloth. Keep the whey for use in another recipe, such as the spent vegetables.