Chop the pineapple into big cubes and grind 4 rings of the pineapple into a fine puree. Keep it aside.
Chop 3 rings as cubes for garnishing and the tomatoes into big pieces.
In a kadai, add oil and splutter mustard seeds.
Once they crack, add jeera, red chilli , curry leaves and saute until they turn golden brown.
Now add chopped tomatoes, curry leaves.
Add the chopped pineapple pieces into the kadai.
At this point, you can add salt, turmeric powder.
Then add rasam powder, cumin powder and jaggery.
Mix everything well.
Add the ground pineapple, required quantity of water and allow it to cook in low to medium flame.
When the rasam starts forming foam, it is done.
Garnish it with chopped coriander.
Serve it with hot rice and papad.