If you are using the optional dry milk powder for a firmer, spoonable yogurt texture, combine 0. 5 cup (2. 3 oz / 65 g) of non-instant, non-fat dry milk powder with 0. 33 cup (2. 6 fl oz / 80 ml) of room-temperature milk in a blender. Process this mixture until it is lump-free and frothy, then set it aside.

In a heavy-bottomed, 3 qt (or 3-liter) stainless steel saucepan, bring the 1 qt (32 fl oz / 946 ml) of whole milk to a quick boil. You must stir the milk constantly with a whisk to prevent it from scorching or sticking to the pan.

Once the milk boils, immediately remove it from the heat. Allow the milk to cool to a temperature of 118°F (48°C). If you are pressed for time, you can quickly cool the milk by half-submerging the pan in a sink filled with cold tap water until it reaches the desired temperature.

While the milk is cooling, prepare your vessel by rinsing a 1. 5–2-quart (1. 5–2-liter) glass, ceramic, or sterilized container with boiling water to sterilize it, then drying it thoroughly.

When the boiled milk has cooled to approximately 115°F (46°C), transfer 0. 5 cup (4 fl oz / 118 ml) of this milk into your sterilized container.

Add 3 tbsp (1. 5 oz / 45 g) of your smooth plain yogurt starter and whisk these two ingredients together until the mixture is perfectly smooth.

Pour all of the remaining cooled milk, along with the prepared powdered milk mixture (if using), into the container with the starter.

Whisk thoroughly to ensure all components are well blended. The target temperature of the entire milk mixture should now be near 112°F (44°C), which is the ideal starting point for setting your yogurt.

Immediately cover the container with a clean towel or a tight-fitting lid and place it into a warm, draft-free environment maintained between 85°F–110°F (29°C–43°C). Good warm nooks include an oven with just the pilot light on, an oven preheated to 200°F (95°C) for 1. 5 minutes and then turned off, or inside a well-insulated styrofoam cooler warmed by a closed jar of hot water. Ensure the environment is not too hot, as this will sour the yogurt before it sets, nor too cold, which will prevent it from setting entirely.

Allow the dahi to set undisturbed for 4–10 hours. You should check the consistency after 5–6 hours; it should be thick and firm, knowing that it will set considerably more once refrigerated. The longer you let it ferment after it is firm, the stronger and more tart the flavor will become.

As soon as the dahi is set to your liking, refrigerate the container, covered. Your Homemade Yogurt DAHI is best consumed within 3 days, although it will remain perfectly safe to eat for 4–5 days, after which it may be used in cooked recipes.

Do Not Disturb the Incubation: Once you have mixed your milk and starter and placed the container in its warm nook, leave it completely alone. Moving, shaking, or stirring the container during the 4–10 hour setting phase will break the delicate protein bonds forming, resulting in a separated or grainy texture.