Add the bay leaves to the milk and bring to a boil in a heavy-based pan on a low heat until it is reduced to half its volume, making sure to prevent it from catching on the bottom of the pan. Remove from the heat and add the powdered patali gud and ground cardamom to the hot thickened milk mix. Remove the bay leaves. Cool to room temperature. Mix in the natural live yoghurt and allow it to set in an earthenware pot for 6 hours in a warm place. Do not disturb the pot or sneak a peek for the six hours that you keep it to set. Once the yoghurt is set, refrigerate and serve cold.
Note: Patali gud is only available in Bengal during the winter months. An easy substitute would be fine brown sugar. It is important to set the mishti doi in an earthen pot with natural yoghurt as the earthen pot absorbs any moisture that maybe released during the setting process.
1 tbsp natural yoghurt
4 bay leaves
1 cup patali gud (or brown sugar)
5 green cardamom pods, powdered