Preparation / Directions:
Toast the cumin, black mustard, and fenugreek seeds, the split dal, and the fresh curry leaves as described below ("Preparing Ground Spices"). Add the peppercorns and chile pods and grind the mixture to a fine powder. Add the coriander and turmeric and mix well.
PREPARING GROUND SPICES:
To toast spices on the stove top, place them in a dry, heavy-bottomed pan and cook them briefly (5 to 7 minutes) over low heat, stirring occasionally, until they darken and begin to release their aromas. Heated mustard seeds will begin to pop, and may jump out of the pan, so have a lid ready. Oven toasting takes somewhat longer; spread the ingredients on a dry cookie sheet and place in an oven preheated to 200 F; stir every five minutes or so. Grind toasted ingredients to a powder with a mortar and pestle, spice grinder, coffee mill (not the same one you use for coffee), or a blender, the pass them through a fine sieve. Transferred immediately to a glass container and stored away from moisture, light, and heat, toasted and ground spices can maintain their flavor as long as four months.
Source: "Lord Krishna's Cuisine: The Art of Indian Vegetarian Cooking" by Yamuna Dev