Heat 50ml vegetable oil in a saucepan with the cumin seeds for 30 seconds.
Add onions to the saucepan and cook until the onions are golden brown, this should take about 8 minutes.
Mix in the ginger and garlic pastes with the green chilli to the saucepan and cook for about a minute.
Add the plum peeled tomatoes to the saucepan and cook for about 2 minutes.
Remove the saucepan from the heat and blitz the sauce until fluffy in texture and a rustic orange colour.
Put back onto a medium heat, add the turmeric, red chilli powder, cumin powder, salt and ghee to the sauce and cook the masala for 8-10 minutes on a low heat, stirring occasionally (add a little water if masala gets dry).
In a separate saucepan, heat 20ml vegetable oil and add the black mustard seeds.
Once the seeds start to pop, add the curry leaves to the saucepan and cook the mixture for about 1 minute.
Add the curry leaves and mustard seed mixture to the masala sauce and cook for about a minute.
Add the water to the masala and boil the curry for about 3 minutes on a medium to high heat.
Add the coconut milk to the curry which will slightly thicken the sauce and cook for 2 minutes before adding the prawns to the saucepan.
Cook the prawns for about 4-5 minutes in the curry, before adding fenugreek leaves, garam masala and coriander to the dish and cook for a final 1-2 minutes.