A little more milk (about 1/3 cup, depending on desired thickness)
Instructions
Heat the Milk: Put the milk in a pot and place it on the stove over high heat. Leave it there until it’s about to boil. When small bubbles appear around the edges, it’s the perfect moment.
Add Vinegar: Add the vinegar immediately.
Stir and Curdle: Immediately grab a spoon and stir very well. The milk will curdle automatically. Stir for only 10 to 15 seconds and wait 20 seconds more.
Cool: Turn off the heat and let it cool a little until it is lukewarm. The green liquid (whey) and the white solid (casein) should be separated.
Separate the Curds: Using a strainer and a pot, separate the liquid green whey from the solid white casein. Do not press to squeeze it completely, as you want the curd to retain a little whey and some acidity.
Blend: Transfer the solids (casein) to a blender. Add the salt and the additional milk. The amount of milk will depend on how thick you want the buttermilk to be. Blend very, very well.
Adjust Consistency (Optional): If the mixture is too thick, you can add more milk (e.g., another 1/3 cup).
Chill and Serve: Turn off the blender. The buttermilk will thicken even more with the cold, so transfer it to the refrigerator and allow it to chill for a few hours until it reaches the desired consistency.