To make curd, Mom always boiled milk for a very long time; until the color of the milk turned into a cream-pink hue.... I had followed her method ever since I started cooking and I continue to do so. A little time consuming, but well worth it! I use 2% milk and here is the secret to a delicious thick curd!
I use steel vessels to boil milk. Rinse the inside of the vessel with just plain water, do not dry the vessel before adding milk. Add milk and place on a small burner, turn the heat on to slightly lower than medium. (This is to avoid milk sticking at the bottom of the vessel) When the milk comes to a boil and a layer forms on top, reduce the heat to right in between low & medium, let boil for 90 minutes. Yes, 90 minutes! Turn the heat off and let cool : In summer, to lukewarm and in winter to a little more warm than lukewarm.
Add a tablespoon of active live culture to the boiled milk, stir well, cover the vessel with a lid and place a bigger vessel (steel or any of our regular saucepans) over the milk vessel, making sure it covers the entire vessel. I just leave it on the stove top... In summers, it takes 4 hours to set and in winters, 4-6 hours. Sometimes, it helps to turn the heat on to medium, only once during the process, for just 30-40 seconds. (Just in case the room temperature has come down, in winters!)
Isn't that a delicious scoop?