In a heavy pan heat 3 tablespoon sesame oil/gingelly oil. Add ½ teaspoon mustard seeds, 1 teaspoon urad dal and as the dal turns golden, add ¼ teaspoon asafoetida and few fresh curry leaves along with 10-12 crushed garlic cloves.
Next add 2 large onions finely chopped. Fry on low flame until translucent.
Now add 3 large tomatoes finely chopped. Cook for 3-4 mins on low flame.
Add ½ teaspoon turmeric powder and salt as needed. Cook for another 3-4 mins.
Next add 1 tablespoon Sambar Powder.
Cook on low flame for 3-4 mins and oil starts to ooze out.
To bring it to the right consistency, add about ¼ to ⅓ cup of water. Mix well.
Cook covered on low flame for 12-15 mins.
When the consistency of the thokku is thick and oil oozes out from sides, remove from heat.
Cool down completely, store it into an airtight container and refrigerate for upto a week. Serve as side dish with idli, dosa, chapati or poori.