Heat a wide pan over low heat.
Add all the whole spices i.e. red chillis, cloves, mace, cumin, coriander, fennel seeds, black peppercorn, cinnamon, big cardamom, small cardamoms. DON'T ADD KASURI METHI.
Roast the spices, mixing it all the time for at least 2-3 minutes or till you get the aroma of the spices.
Switch off the heat.
Add kasuri methi and all the powders i.e. turmeric, nutmeg, ginger, amchur powders. Mix well.
Transfer the mixture to a plate to allow the spices to cool down a bit. Don't leave it in the hot pan as the spices may get burnt.
Using a spice or coffee mill, grind the spices to a fine powder.
Store Tandoori Masala in an airtight jar.