Special equipment: a spice grinder
Whisk together the chile powder, paprika, cayenne, ginger, salt, garlic powder, onion powder and nutmeg. Set aside.
Put the cardamom, coriander, fenugreek, allspice, cloves and cinnamon in a small skillet and toast over medium-low heat, shaking the pan regularly, until fragrant, about 4 minutes. Cool slightly.
Grind the toasted spices in a spice grinder to a fine powder. Add to the chile powder mixture and whisk to combine. Sift the spice mixture onto a piece of parchment paper, return to the bowl and whisk again. Return the pieces left in the sifter to the spice grinder and grind again as finely as possible; whisk into the spice mixture. Transfer to an airtight container and refrigerate until ready to use.
You can make the spice mix hotter or milder by varying the amount of cayenne.