Dry fry coriander seed for 3 minutes in a skillet. Roast the cumin in the same way. Grind together, coriander, cumin and peppercorns. Set aside. Add lemon grass, cilantro, ginger and lime peel to food processor, process to a paste. Add garlic and shallot and process some more. Add chilies and process. Remove from processor and stir in ground spice, salt and shrimp paste.