Sauté the bay leaves, cardamoms, cloves, fennel seeds, cumin seeds, coriander seeds and the red chillis in a thick bottomed pan on medium heat till aromatic.
Put them in a blender jar when cool, add the ginger garlic paste, vinegar and tamarind paste and grind to a thick paste. Add a little water if necessary.
Place the jackfruit, mushrooms, and potato in a large mixing bowl. Add the marinade paste, turmeric and salt and toss it till all the pieces are coated. Let it rest covered for 20 to 60 minutes.
Heat 2 tbsp oil in a thick bottomed pan, add the cinnamon sticks and sliced onions and sauté till the onions are soft, translucent and a light brown.
Add the marinated vegetables, sauté for a minute and then cover and cook for 5-7 minutes.
Add the sugar and a little water if necessary and cook for 10-15 minutes or till the potatoes are cooked.
Serve garnished with coriander.