Cardamom, a native spice of southern India, is one of the most expensive spices due to the finicky nature of its cultivation and harvest methods. While cracking open cardamom pods to release seeds for grinding is more laborious than simply buying preground cardamom powder, powder tends to lose essential oils and flavour faster than whole pods and seeds. The tools for crushing cardamom seeds are very minimal as the process requires more wrist strength than gadgetry.
Hold a cardamom pod over your mortar and gently squeeze the pod between your thumb and forefinger to crack it open. If the pod is green and difficult to squeeze open, place it into your mortar and gently crush it open with your pestle.
Open the pod shell and let the seeds fall into the mortar. Any seeds that continue to cling to the inside of the pod shell can be easily scraped out with a fork tine. Cardamom seeds are tiny and very light; give them a gentle scrape out of their shell so that they don't fly all over your kitchen counter or table.
Each pod should contain between 17 and 20 little seeds. Given the strength of the essential oil in cardamom seeds, you may not need to break open many pods.
Repeat this process until you have the desired number of cardamom seeds in your mortar and ready to grind.
Toss out the shells if not needed for your recipe. Some recipes, such as curries and stews, may call for the cardamom pod shells to be included in the cooking as well. If used, they will eventually disintegrate into the dish you're cooking.
Crush the seeds with the heavier, rounded end of your pestle. A firm, slow grinding motion is all that is needed to pulverise the seeds.
Unless the recipe you're following specifically calls for finely ground cardamom --- in which case you may want to use a high-powered spice grinder --- just aim for a coarsely ground consistency. This should only take a few minutes of grinding.