Thinly slice the onion. Heat 1 tablespoon of oil in a pan. Add sliced onion, curry leaves, and some salt. Salt absorbs moisture from the onion and helps the onion to cook faster.
Sauté the onion until it turns brown. Add oil if needed. ** The onion should be well sautéed in this recipe. So never compromise on this step. Grind ginger and garlic into a fine paste. Add ginger and garlic paste. Add 1 teaspoon oil and sauté it well.
Add turmeric powder, chili powder, pepper powder, coriander powder, and garam masala to the above mix. Add 2 teaspoon oil and sauté it well until it releases a pleasant aroma.
Slice tomatoes. Add it to the above gravy and mix well. Cover and cook for around 5 minutes, or until tomatoes are cooked. Add enough salt. Add cocum / kudampuli.
Add cleaned prawns and mix well. Cover and cook until prawns is done.
Prawns itself has water in it. Ideally, prawns should get cooked by the time water gets dried up. I like to add some coriander leaves at this stage. It's optional. Remove cocum. Otherwise, it might become over sour.
Once the prawns are cooked, open the lid. Sauté it until the consistency you desire.
Notes
Slicing onions thinly is important. It helps them cook evenly and blend well into the masala.
Be patient while cooking the onions. Slow cooking brings out more flavour. Don’t rush this step.
If you are making this in bulk, a lot of onions might release water while sautéing. This is normal. Just keep cooking until the excess moisture evaporates. Stir occasionally to prevent the onions from sticking to the bottom of the pan.
Cook prawns just right. Overcooked prawns turn rubbery, and undercooked ones feel raw and unpleasant.
Add freshly ground pepper at the end. It gives a sharp, warm finish and lifts the flavour of the dish.