Take 1 litre of full-fat milk and heat it in a heavy-bottomed pan. Bring it to a boil and then reduce the heat to low, allowing it to simmer until it reduces to half its original volume.
Add 200 grams of sugar to the reduced milk and stir well. Continue to cook on low heat until the sugar dissolves completely. Turn off the heat and let the milk cool down to lukewarm temperature.
In a separate bowl, whisk 200 grams of fresh curd until smooth. Gradually add the lukewarm milk to the curd, mixing well to combine.
Preheat your oven to 100°C. Pour the milk-curd mixture into a heatproof earthenware or ceramic container. Cover the container with a lid or aluminium foil.
Place the container in the preheated oven and let it cook for 1-1.5 hours, or until the doi sets and achieves a thick, creamy consistency.
Once the mishti doi is set, remove it from the oven and let it cool to room temperature. Then, refrigerate it for at least 3-4 hours before serving.