Heat the milk – Warm it in a pot until it's hot but not boiling (about 180°F or 82°C).
Cool it down – Let it cool until it's warm (about 110°F or 43°C).
Add yogurt – Stir in the plain yogurt and mix well.
Let it sit – Pour into a jar, cover, and keep in a warm place for 6–12 hours (like an oven with the light on or wrapped in a towel).
Check & refrigerate – Once it's thick, place it in the fridge for a few hours before eating.
