Put the milk in a large pot. Set the heat to high until the milk just starts to boil. Immediately remove the milk from the heat. This is important! You have to watch the milk, otherwise, you will run the risk of the milk boiling over and making a mess. The reason why we boil the milk is to kill competing bacteria so that the yogurt cultures can grow.

Let the milk cool down to a temperature that you can stick your finger in for 10 seconds. If the milk is too hot, then come back until you can keep your finger in the milk for 10 full seconds.

Mix the starter yogurt with 2 cups of warm milk (from the pot) in a separate bowl. Mix until smooth. Add the milk and starter yogurt back to the pot full of milk.

Cover the pot and wrap it with a towel. Let the yogurt sit at room temperature for a full 24 hours. For more sour yogurt, let the yogurt sit at room temperature for 48 hours. Don't exceed 48 hours.

Place a thick paper towel (add 2 layers of the paper towel) in a strainer. Place the strainer on top of a large bowl. Add the yogurt on top of the paper towel or cotton cloth fabric. The bowl will capture the whey as it drains from the yogurt. The whey is a yellowish color which is perfectly normal.

Strain the yogurt for around 6 to 8 hours. You can strain the yogurt at room temperature or in the fridge, whichever, you prefer.