To make the soup in an Instant Pot (IP):
Switch on the IP, put the coconut oil in the inner and press the saute button. When it's hot, add the onion and saute until it's softening (8-10 min). Add the garlic, ginger, chillies and apple and cook for a further 2 minutes, stirring.
Stir in the spices and cook for 2 minutes (add a little water if they start to stick). Stir in the soaked, drained and refreshed split peas (see Recipe Notes) and the desiccated coconut and saute for 1 minute. Add the stock or water and stir. Press the Keep Warm/Cancel button.
Lock on the lid, making sure the lever points to 'sealing'. Press the Manual button and, using the + or - button, change the time to 25 minutes. Leave until the time has elapsed and the indicator has counted down to zero. Switch off and leave until the pressure has naturally released. Switch the lever to 'venting' then carefully remove the lid.
Check if the split peas are very soft and starting to fall apart. If not, cook for a further 5 minutes and repeat. Switch off the IP.
To make the soup on the stove:
Put the coconut oil in a large saucepan over a moderate heat. When it's hot,add the onion and saute until it's softening (8-10 min). Add the garlic, ginger, chillies and apple and cook for a further 2 minutes, stirring.
Stir in the spices and cook for 2 minutes (add a little water if they start to stick). Stir in the soaked, drained and refreshed split peas (see Recipe Notes) and the desiccated coconut and saute for 1 minute. Add the stock or water and stir.
Put on a lid and bring to the boil. Take down to a simmer and cook gently until the split peas are very soft and starting to fall apart (35-50 min). Take off the heat.
Using a stick blender, puree the soup until smooth. Add more stock for a thinner soup. Taste and season with salt plus more garam masala if needed.
Just before serving, stir in the chopped coriander (reserve a little to scatter over if liked), ladle the soup into bowls and swirl some coconut milk over each one. Top with spiced, fried potato matchsticks and the reserved coriander if liked.
Heat the oil in a small wok, saucepan or deep fryer.
Drain the soaked potato sticks in a sieve and run fresh tap water through them. Dry thoroughly in a clean tea towel.
When the oil is hot, carefully add the dry potato sticks and cook until browned and crispy. Cook in batches if necessary.
As each batch is cooked, transfer to kitchen towel to drain for a couple of minutes then sprinkle with the spices and salt. Set aside until the soup is ready.
Sprinkle over the soup when serving.