Make the rempah paste by putting all the ingredients in a food processor and blend into a smooth paste.
In a heated pan, add 2 tbsp oil and fry the rempah paste until it turns dark red in color.
Add the prawns and mackerel paste to the food processor and blend together with the rempah.
Thinly slice the kaffir leaves and add them to the mixture. Mix well.
Put two banana leaves together and brush the leaves with some oil.
Scoop one tbsp of the otak mixture onto the oiled surface and secure the two ends with toothpicks.
Grill in oven for 20 mins at 200c.