Add the butter to the instant pot and set on saute. When its melted add the onion and cook until softened (around 3 minutes).
Add the garlic, ginger and chili. Stir together.
Now add the garam masala, ground coriander, ground cumin, turmeric, smoked paprika, chilli powder and salt (smells amazing!).
Add the diced chicken. Stir well to combine (no need to brown).
Add the tinned coconut milk, tomatoes, tomato puree and chicken stock. Stir thoroughly before putting the lid on the instant pot and setting on manual, high pressure for 15 minutes. Leave under pressure for a further 10 minutes and then do a quick release and remove the lid.
Set the instant pot to saute. Add the cornflour to a jug and remove around 5 tablespoons of the liquid from the instant pot. Mix well and add back to the instant pot. Stir well whilst the sauce thickens (around 2 minutes).
Serve and garnish with the coriander.