Pour the milk in a pot and heat it until it almost boils. Let it simmer for about 5 minutes.

Let the milk cool down to 40 to 45°C (110°F). I don't use a thermometer, but touch the milk - when it's hot, but you can still touch it without burning yourself, it's the right temperature.

Put the yogurt in a big jar and add a little milk. Stir with a spoon.

Add the rest of the milk and stir well.

Close the jar and cover it. I usually wrap it into two towels and a blanket.

Leave the jogurt alone for at least 12 hours. Then unwrap the jar and put it into the fridge.