Sinhalese unroasted curry powder is called amu thuna paha (literally, raw three-five). The name refers to the three to five spices that unroasted curry powder traditionally contains. The three essential spice seeds include cumin seeds, fennel seeds, and coriander seeds, and additional curry leaves and/or pandanus leaves, and cinnamon bark.
In a dry (not oiled) frying pan over low heat, lightly roast the cumin, fennel, and coriander seeds together just long enough to release their fragrance and remove any moisture. Shake the pan to roast the spices; you may also use a wooden spoon to stir continuously in the pan. Remove them from the pan and set aside to cool.
In the same pan over low heat (no need to clean the pan), dry-roast the curry leaves and cinnamon together for 2–3 minutes, until the curry leaves are crispy.
Let all the ingredients cool, and then put them into a spice or coffee grinder (this may have to be done in batches). Grind the spices to a fine powder. Spoon the curry powder into an airtight jar or container and store in a cool, dark space for up to 2 to 4 months.