Put the liter of milk in a saucepan and bring it to a boil. Once the milk begins to boil, turn off the heat.
Add the vinegar and stir very well until the milk separates into whey and curds.
Using a fine sieve, remove all these curds from the saucepan, you can use a tablecloth to help you, if you prefer.
Transfer these curds to a blender and blend together with the butter and one pinch of salt, gradually add the milk until you get the right consistency (a creamy cheese spread consistency).
Transfer to a bowl or pot and take it to the fridge for at least 3 hours.