Dahi (plain yogurt)
4 cups whole milk
1 tsp plain yogurt
1/2 cup dry milk
1. Heat milk over low heat in a heavy bottomed pan. If the milk sticks, add a cake rack under to pot to prevent the sticking. After about 40 minutes when the milk starts rising, remove from heat.
2. Let it cool down to 115 degrees F, or about ½ hour at room temperature.
3. Add the plain yogurt and dry milk. Mix well and transfer to a glass bowl. Keep the bowl in a warm spot (85°F) by the stove for about 6-7 hours. If the room is cooler, warm the oven for 5 minutes, then put the glass bowl inside. If you have a gas range, you need not warm the oven; simply leave the pilot flame on.
4. Leave at this setting for about 6-7 hours or until the mixture sets. For sour yogurt, leave it setting longer. Refrigerate the yogurt until use.
Source: Afshin from Kokila pre-1983