In a heavy bottom pot add a little splash of water. This will prevent milk from sticking to the pot.
Add 4 cups of milk.
Bring the milk to one full boil. Take it off the heat. The milk will be about 180F.
Let the dahi come between 115F-120F. This means just warm enough to stick your finger in the milk. Froth the milk at this stage if you like a frothy layer on top. Read the tips to do this.
Whisk the yogurt starter smooth. Add to the milk once it is warm enough to dip your finger in the milk.
Mix it well. Transfer it in desired stainless steel or glass bowl. Cover and let it set for 5-8 hours in a warm place.
I use clay pot to set my dahi, but you will have to season it. This means that you soak the clay pot in water overnight. The next morning you let it dry completely in the sun. Once dried, add oil and heat it on a high flame. Once cool, your clay pot is ready to use.