First for tamatar chutney , puree almost 3 tomatoes and then add in a pan and cook on a medium flame with pinch of salt , 1/4 tsp black pepper powder and 1 tbsp jaggery powder. You can adjust sweetness as per your taste. 

Keep cooking till it reaches a thick consistency and is not very watery and then keep it aside.

Now heat up some oil and add cumin seeds, green chilli and 1 tbsp ginger and saute for few seconds and then add around 3 chopped tomatoes and cook on medium flame.

As tomatoes turn mushy add two medium sized mashed potatoes and mix it well.

Add black pepper, chilli powder, salt, cumin powder and chat masala to this mix and keep mixing it well.

Cook this mixture for around 10 mins till all tomatoes and potatoes are mixed uniformly. You can also use a little of tamatar chutney to add in this.

Add 1/2 tbsp of jaggery and 1/2 lemon juice in the mixture so its spicy, tangy as well as sweet.

Now take a serving bowl and first all the tomato and potato mixture and top it up with tamatar chutney, coriander leaves, some chopped ginger, chopped green chilli and then crushed namakpare to complete the entire preparation.