If you don’t have whey, make it yourself first. Heat the milk until it starts steaming. Now add 3 tablespoons of lemon juice and mix well with a wooden spoon. Take the pot off the stove, cover it with a towel and let it stand for 1 hour. During this time, the curds will separate from the whey.
The solid part is now cream cheese, which you can use elsewhere. Scoop it out, add some heavy cream if necessary and let it drain further in a fine-mesh sieve. Wrap it up and keep it in the fridge. Use the remaining whey for the ricotta.
2. Ricotta from whey
Put the whey, whole milk and salt in a saucepan and heat them up to about 80° C (175° F) over medium heat. It is best to check the temperature with a kitchen thermometer.
Cautiously stir in 1 tablespoon of lemon juice with a wooden spoon until the mixture's temperature reaches 90 °C (190°F). Do not let it boil! Stir the bottom of the pot well. After around 30 seconds the milk coagulates and flocculates.
In the meantime, line a colander with a cheesecloth or clean tea towel.
Now skim off the milk flakes from the surface with a slotted spoon and put them into the lined sieve. When all the milk flakes have been skimmed off, leave them sit for a around 10 minutes. Then fill the finished ricotta into ricotta molds and chill well.
After 3 hours in the fridge you can eat or process the ricotta.