Sri Lankan Chicken Curry

Name: Sri Lankan Chicken Curry
Ingredients: 3 pounds chicken pieces; 3 tablespoons lemon juice; 6 cloves garlic & 1 inch ginger root, crushed together; 2 teaspoons salt; 1 tablespoon black pepper; 1 tablespoon Sri Lankan curry powder; ½ tablespoon cayenne pepper; 4 cardamoms; 2 cloves; 8 curry leaves; 1 inch cinnamon stick; 1 medium onion, sliced; 3 tablespoons vegetable oil; ½ can tomato paste or tomato sauce; 1 cup chicken stock or water; 1 cup thick coconut milk or fresh milk; ½ teaspoon turmeric powder; 1 piece of lemon grass (optional)