Garam Masala is a blend of spices and sometimes herbs. The word masala means spices and garam means hot. The hot is in the Ayurvedic sense of heating the body, not blow your head off chilli heat. It differs from region to region and many families have recipes that are handed down through generations.
Recipe for Garam Masala
3 Tsp Cumin seeds
3 Tsp Fennel seeds
1.5 Tsp Cardamon seeds (not the pod)
0.5 tsp Black onion seeds (also called Nigella or Kalonji)
0.5 tsp black peppercorns
2cm cinnamon stick
Put everything in a dry frying pan and gently toast. Once you smell the gentle fragrance tip onto a plate and cool.
Put The cooled spices into a spice grinder and blitz to a powder.
Store in an airtight container.
I have a grinder I only use for spices. If you do not have a spice grinder use a pestle and mortar. If you use your coffee grinder you will likely taint it and have a garam masala blush to your coffee. I have heard a wipe out with white vinegar (sparingly on kitchen paper) will get rid of the smell. Obviously I have not tried it so it is at your own peril.