Rinse Sabudana 3-4 times in running water until all the starch is washed away. You can use a colander while rinsing.
In a glass bowl, add 1 cup of fresh water just to submerge the pearls and soak them for 3 hours.
After 3 hours, sabudana is all puffed up with no water and is soft and non-sticky. In case you see some water, using a strainer or colander, strain all the water from the sabudana pearls. Do check if the Sabudana can be smashed by pressing a pearl with your fingers.
Dry roast the peanuts until you see that the skin gets brown, and peels off easily. Keep the peanuts aside to cool.
Coarsely grind 5 - 6 Tbsp of roasted peanuts.
Add the peanut powder to Sabudana, then mix well and keep aside.
Set a pan on medium-high heat, and add oil/ghee, mustard seeds, cumin seeds (jeera), turmeric powder, roasted peanuts, curry leaves, and chopped green chillies, then sauté it on a medium flame for 1-2 minutes.
Add cubed boiled potatoes and salt, and mix well. Continue to sauté it for a minute.
Add puffy pearls, then combine well and close the pan. Allow it to cook for 5-8 mins on a medium-low flame (stir occasionally).
Cook for another 3- 4 minutes with the lid open (this is to avoid water vapor deposit from the lid).
Once it is perfectly cooked, switch off the flame, and garnish it by adding freshly chopped coriander leaves and some freshly squeezed lemon juice.
Your Sabudana khichdi is ready to be served hot!