• The first step is to peel the skin of tomatoes. This step is optional. I have made this thokku both ways tomatoes with skin and tomatoes without skin. If you decide to peel the skin, proceed to next step if you chose to skip, blend the tomatoes directly.

To peel the skin of the tomatoes

• Wash the tomatoes well with water. In a big pot, bring 8 -10 cups of water to a boil. Add the tomatoes to the water and take it off the stove.
• Keep it covered for 30 minutes. I used my 8 liters cooker vessel for this.  The water level should be well above the tomatoes.
• After the given time, using a ladle, scoop the tomatoes out of the hot water. Be careful, since the water would be very hot.
• Let the tomatoes rest for while, then peel the skin of the tomatoes.  Take the peeled tomatoes in a blender and blend until smooth. I used my hand blender and blended it straight in the vessel itself.

Make the Spice powder

• In a small tadka pan, dry roast the ingredients given under "roast n grind" and keep aside to cool. When it is cool enough to grind, take it in the small jar of your mixie and grind it to powder. Keep aside until use.

Let us make the thokku

• Heat a heavy bottom pan, add oil given under "Tempering", splutter mustard seeds, add hing, turmeric powder.
• Now slowly add the pureed tomatoes to this tadka. Be careful, the liquid might splutter out. 
• Mix well. Reduce the flame to medium and let it cook. When it comes to a boil, add the ground powder and salt. Mix well.
• Let this cook until the liquid is absorbed completely and oil separates on top. Takes about 40-50 minutes for the above quantity. 
• Once done, the thokku/preserve will come away from the sides of the pan and move along with the laddle as you mix it.
• Take it off the stove and let it cool completely. Store in an air-tight container in the refrigerator. 
• An apt combination for idly/dosa/chapathi, that too while travelling this preseve stays good for a day or two in room temperature. But remember to use a clean and dry spoon always. Stays well for weeks, while refrigerated.