Line an 8 x 8 inch pan with parchment paper sling.
Crush the pistachios and cardamom using a mortar and pestle or a spice grinder into a fine powder.
Melt (or warm) half the ghee in a heavy bottomed nonstick pan (I use cast iron) on medium heat.
Add all of the besan and mix well while adding the rest of the ghee in small portions.
Stir in the pistachios, cardamom and the sugar.
Keep stirring for the next 20-30 minutes on low-medium heat. The besan will clump up at first. After around 10 -15 minutes, the besan will start to loosen up and eventually become smooth. Keep stirring until the besan turns aromatic and has changed color slightly. If you are not sure, taste a pinch of the mixture, if it tastes bitter, you need to stir for a few more minutes.
Transfer the mixture to the prepared pan. Tap the pan to get rid of excess air.
Sprinkle pistachios/sliced almonds/cashew nuts on top for garnish.
Let the burfi set for 2-3 hours (stick the pan in the refrigerator after 10-15 minutes on the counter for quicker setting) and then cut into pieces.
These burfis can be stored on the counter in an airtight container for a week or longer in the refrigerator.