Preparing the arbi / colocassia for the curry / korma: Wash the colocassia well. Place some water in a pressure cooker. Place the colocassia in a bowl that fits into the cooker with 1/4 cup water. Pressure cook for 2 whistles and then on sim for 5 minutes. This also depends on the size of the colocassia so choose medium sized ones and all roughly the same size.
Once the cooker cools, open and allow the cooked colocassia to cool. Peel and cut in half, lengthwise.
Toss them in a bowl gently with 1/2 tsp salt and 2 tsp oil.
In a preheated oven or airfryer (200°C) bake them until golden brown outside. This will take roughly 10 minutes in airfryer and 20-30 minutes in an oven.
Once done, remove from airfryer / oven and keep aside.
Frying the onions: Peel the onion, halve it and chop it into very thin slices. Separate each slice so as to get thin segments of onion. In a pan, take enough oil and deep fry the onion segments on a low heat until golden brown. This is a time consuming process and takes up to 20 minutes for one onion.
Alternately, air fry the onion segments. Toss onion segments in few drops of oil and place them in preheated airfryer (180°C) or 6-8 minutes until golden brown and crisp.
Once the fried (or air fried) onions are cooled, crush or blend the browned onion segments to a fine powder.
Preparing the paste: In a small jar of the mixer, puree the ginger, garlic and roughly chopped onion to a fine puree. Keep aside.
Toasting the coriander powder: On a tava or in a small pan, toast the coriander powder until aromatic and keep aside.
Making the korma: In a heavy bottomed pan, place the remaining oil along with the ghee. Immediately add the whole spices, even before the oil is hot. You don't want the spices to puff up in this recipe.
Add the onion-ginger-garlic paste and fry on a medium heat for 4-5 minutes.
Add the toasted coriander powder and fry for another 2-3 minutes.
Whisk the crushed fried onion powder along with the yogurt and add it to the pan, with the flame on lowest setting or the yogurt will separate.
Add the salt, red chilli powder and bring to a gentle simmer.
At this stage add the 'fried' arbi halves, add 1/4 cup water if the sauce is too thick, and bring to a gentle simmer.
Traditionally, these kormas are not garnished with coriander, you may garnish with a few fried onion segments. Serve with parathas.