Cool the Milk - Remove the saucepan from the heat and allow the milk to cool to 110–115°F (43–46°C). To speed up the cooling process, place the saucepan in a cold water bath, stirring occasionally. Make sure the milk has cooled sufficiently before adding the starter, as excessive heat can kill the beneficial yogurt cultures.

Add the Yogurt Starter - Place 2 tablespoons of plain yogurt containing live and active cultures into a small bowl. Add a few tablespoons of the warm milk and whisk until smooth. Pour this mixture back into the saucepan and gently stir until evenly combined.

Incubate the Yogurt - Pour the milk mixture into a clean glass or ceramic container and cover with a lid or plastic wrap. Keep it at a steady temperature of approximately 110°F (43°C) for 6–12 hours. A yogurt maker works well, or you can use an oven with the light on if it stays at the right temperature. Avoid moving or stirring the yogurt while it incubates.

Check for Doneness - After 6–8 hours, gently check the yogurt. It should have a soft, custard-like consistency and a pleasantly tangy aroma. If it is still too thin or you prefer a tangier flavor, continue incubating for up to 12 hours. The longer the yogurt incubates, the tangier it becomes.

Refrigerate the Yogurt - Once the yogurt has set, transfer it to the refrigerator without stirring. Chill for at least 2 hours, preferably longer, to allow it to firm up completely. The yogurt will continue to thicken as it cools.

Make Greek Yogurt (Optional) - For thicker, Greek-style yogurt, line a fine-mesh strainer with several layers of cheesecloth and place it over a deep bowl. Pour the chilled yogurt into the cheesecloth and refrigerate for 2–4 hours, allowing the excess whey to drain into the bowl. For easier draining, gather the corners of the cheesecloth, tie them securely, and suspend the bundle over a bowl in the refrigerator. The longer you strain it, the thicker your yogurt will become.

Flavor and Serve - Once chilled, stir the yogurt until smooth and creamy. Enjoy it plain or sweeten it with honey, vanilla extract, or fresh fruit. Store any leftovers in a covered container in the refrigerator.