Normally we use broad mouthed pan to make rabri, but you can also make it in your regular pan just as i did. Make sure that the pan is deep and heavy. Pour milk into the pan and let it boil. Once the milk starts to boil, lower down the flame.
As soon as the layer of cream appears at the top of the milk shift it towards the rim. Do the same with the next layer of the cream when it appears. If you will rotate a fan or any paper over the pan, then the layer of the cream will appear faster.
Keep on making the layer of the cream and collect it at the corners of the pan. The cream layer collected at the corners of the pan will start to dry and become thick. Once a thick layer of the cream get accumulated at the rim and the milk reduces to 1/3 add sugar, chopped pistachios and cardamom into the milk. Turn off the flame and take out the cream (also called khurchan) with the spoon and mix it into the milk. Do not stir much after adding the cream into the milk and let it be as it is.
Rabri tastes best when the khurchan remains tasteless from inside. Rabri is ready. Take it out in a serving dish and refrigerate so it gets chilled. Rabri tastes better when served chilled.