Heat 1 teaspoon of vegetable oil in a heavy pan over medium heat.

Add mustard seeds, fenugreek seeds, cumin seeds, black peppercorns, and coriander seeds.

Stir and roast for 3-4 minutes, reducing heat if necessary to avoid burning.

Add asafoetida and turmeric powders, stir, and remove from heat.

Transfer spices to a bowl to cool.

Heat the remaining 2 teaspoons of vegetable oil in the same pan.

Roast channa dal, urad dal, and toor dal for a couple of minutes until they start to color.

Add curry leaves and dried red chilies and continue roasting until the chilies have darkened, being careful not to burn.

Add the lentil and chili mixture to the bowl with the other spices and cool completely.

Grind the spice mix in small batches in a clean coffee grinder until finely ground.

Store the Sambhar Masala in a tightly closed jar away from heat and sunlight for several months up to a year.