The first step is to cook the potatoes. Wash the potatoes thoroughly and pressure cook them for 3-4 whistles. When the potatoes are in a mashable consistency, they are ready. Mash the cooked potatoes and keep them aside. Next, place a pan on medium-high heat and add a tablespoon of oil.
Once the oil is warm, add the mustard seeds and allow them to sputter.
Add the chana dal and allow to roast for a bit until slightly golden.
Follow it up with the green chillies, curry leaves and ginger. Saute for about 30 seconds.
Next, add the onion and saute them along with the rest of the spices until they are soft.
You can add half a teaspoon of turmeric powder and the two tablespoons of Sagu Masala powder at this stage and give it all a good mix. Saute for under a minute.
Add the mashed potatoes and season with salt. Start off with half a teaspoon and adjust accordingly later.
Since sagu is a gravy-like dish, add half a cup of water (preferably warm). Mix all the ingredients well and allow it to simmer on a low flame for the couple of minutes.
Finally turn off the flame, and garnish with finely chopped coriander leaves and a juice from a full lemon.
Your potato sagu is ready to be served with pooris or rava idli.