In a bowl sieve the whole wheat flour, chickpea flour, coco powder and baking powder.
In another bowl take powdered jaggery and add ghee to it.
Add this jaggery ghee mixture to the bowl of dry ingredients and rub until it appear like bread crumbs.
Add milk little by little as required and make a dough. Do not knead, just gather the flour together.
Meanwhile preheat the pressure cooker. For that take a 5 liter old pressure cooker and add 2 cups of salt or fine sand. Place a stand over it. Remove the whistle and rubber gasket from the lid of the pressure cooker and close the lid. Heat the pressure cooker on medium to high heat for about 15 minutes.
Grease a plate with ghee. Select the plate size which fits well inside the pressure cooker.
Pinch out 10-12 equal sized portions of the dough. Roll each portion between the palms and then flatten slightly.
Add a little chopped pistachio in the center of each cookie dough and apply slight pressure.
Arrange the nan khatais on the greased plate such that they do not touch each other. Keep enough space between them as they spread out while baking.
Carefully place the plate of Nan khatai in the preheated pressure cooker over the stand. Close the cooker, on a low to medium flame, allow the Nan khatai to cook for about 20 minutes.
Allow the nan khatai to cool down on the rack before transferring them to an airtight container.
The chocolate nan khatai remains good for about 4-5 days at room temperature in an air tight container.