Heat olive oil in a pan. Add garlic, pumpkin, onion, carrot and leek and sauté. Add bay leaf and continue to sauté for two to three minutes. Heat another pan. Add prawns heads and two cups of water and let it boil. Reduce heat and let it simmer. Place the prawns one on top of the other and wrap in a piece of aluminium foil drop this into the pan with prawn heads and water and let it cook.
Add a cup of water to the vegetables and cook till soft. Add tomato along with celery, black peppercorns and salt. Mix and cook for one minute. Remove the bay leaf and transfer the mixture into a blender. Blend to a smooth puree. Remove the scum from boiling prawn stock. Heat butter in another pan. Add refined flour and sauté for one minute.
Add prawn stock little by little and stir well to avoid lumps. Add the vegetable puree and cook for one to two minutes. Strain into a deep pan. Bring the mixture to a boil again. Transfer this into a serving dish. Unwrap the prawns and place it in the centre. Sprinkle saffron strands and serve hot.