Make sure all your ingredients are dry and moist free. To ensure you can also sun dry red chili powder and turmeric for some time. Wash tomatoes under running water and leave them aside to dry.
Bring 4 to 6 tbsp water to a rolling boil. Allow the temperature to cool down and then soak tamarind in it. You can also skip this step and add tamarind directly to the tomatoes. But most times tamarind is not clean so soaking and filtering is needed.
Dry roast fenugreek seeds on a low flame till they emit a nice aroma. if using mustard add them and fry just for a minute and set aside to cool.
Powder the roasted fenugreek seeds and mustard.
Making tomato pickle or pachadi
Chop tomatoes and fry them with salt and turmeric in a pan on a medium flame till they turn mushy. The pulp should thicken.
Squeeze the tamarind fully with your fingers & filter it to remove the impurities & pulp. Add this to the cooked tomatoes. Adjust the tamarind to suit your taste. Mix and cook well for 5 mins until the mixture bubbles up very well.
When the mixture cools down completely, add chili powder, salt, fenugreek and mustard powder and mix well. Check salt and spice. Add more if needed.
Tempering tomato pachadi
Heat a pan with oil. Add mustard, fry till they splutter, add garlic. Fry till they turn aromatic, add red chilies and curry leaves. Fry them until they turn crisp. Add hing.
Turn off the stove. Transfer the tomato pickle to the pan and mix well.
Cool the tomato pickle completely. Store this in a air tight glass bottle.