In a saucepan, pour the milk and the yogurt.
Place the saucepan over medium heat until the temperature reaches about 190 F (90 C). Use a thermometer to check the temperature. A higher temperature is ok, but don’t let the milk boil.
Line a colander with cheesecloth.
Stirring the milk will let you see the separation between the solid cheese lumps and the grayish liquid when the cheese begins to form.
After the lumps begin forming, keep the saucepan on the heat 4–5 minutes longer to allow the cheese to fully coagulate.
Turn off the heat. Using a strainer, remove the cheese and place it in the colander. Lightly press the surface of the cheese to facilitate the elimination of liquid.
Leave the ricotta to drain until no more liquid comes out, but don’t over-drain it or the cheese will be too dry. If the ricotta turns out to be too granular, place it in a food processor and run the blade until it’s smooth before using it in a preparation.