1. Using a small spice grinder or small electric coffee grinder, grind mustard seeds and coriander seeds.
2. With a mortar and pestle, mix together the garlic, Garam Masala, ground mustard seeds and coriander seeds, ginger, cumin, and red pepper. Pound it all into a paste.
3. Heat the vegetable oil in a skillet. Add the bay leaves and onion. Saute until the onion is translucent. Add the ground paste and cook until the oil separates, about 15 minutes.
4. Add the coconut milk to the sauteed onion, along with the tamarind paste. Bring to a boil, then simmer over medium-low heat for 15 minutes.
5. Add the prawns and salt and simmer until done to taste, about 5 minutes.
