Remove the mint leaves from the stem and keep them aside. Now wash the leaves well to remove any dirt sticking to them. I use my kitchen sink to wash the leaves when I am working with larger quantities. I seal the drain and then fill the sink with water and wash the leaves. Then let the leaves sit in the water to allow the dirt to settle down. After few minutes, carefully remove the leaves without disturbing the dirt.
Now place the washed leaves in a clean kitchen cloth and let it air dry.
Heat a teaspoon of oil in a pan and add the urad dal, coriander seeds, fenugreek seeds, pepper corns and cumin. Fry them until it turns aromatic (about 30 seconds).
Now add the dry red chili and fry for 30 seconds more. Next add the tamarind and stir once and turn off the flame. Let the tamarind soften a bit in the heat.
Place the cooled fried ingredients in the blender jar and coarsely grind it.
In the same pan, add ½ teaspoon of oil. Add the washed and dried mint leaves and saute it in low heat for just about a minute until the leaves starts to wilt. Take it off the heat and let it cool down.
Add the mint leaves to the blender with the ground spices and grind it into a paste adding no water. Add salt when grinding. You can keep the paste slightly coarse like I did or grind it smoothly.
In the same pan heat about 4 tablespoon of oil and once the oil heats, add the mustard seeds and turmeric powder. When the mustard seeds crackle add the ground paste and mix well.
Cook the mint thokku on low heat. Add the brown sugar / jaggery if using and continue to cook. In about 10 minutes or so, the pudina thokku would appear to form a mass and would begin to ooze out oil. Turn off the heat at this stage.
Store the cooled mint thokku in a clean glass jar and refrigerate for longer shelf life.