Into the same pan, add onions and cumin.
Add the salt to quicken the cooking.
Add the rest of the ingredients to the pan once the onions turn slightly brown.
Stir through and add the water.
Bring it to boil, lower the heat to medium and cover until the tomatoes' skin comes off easily. About 10 to 15 minutes.
Switch off the heat and let it cool for at least 10 minutes.
Transfer all the ingredients of the curry into a blender and blend until smooth.
Pass the curry through a sieve.
Heat the pan up again and add butter, and once it melts, add the sieved curry.
When the curry is boiling, adjust the taste with salt and ground chilly or fresh chillies.
Add water if the curry is too thick.
Add the prawns and once it boils again, boil it further for another minute or two (depending on the size of your prawn/shrimp)
Scoop it up! And top with cream.
Top with coriander/chilies/anything! and serve with roti, naan, rice etc.