Dry roast cumin seeds and coriander seeds in a non-stick pan till fragrant.
Transfer the roasted spices in a mortar. Add ginger, garlic, red chilli powder, turmeric powder and grind into a thick paste using a pestle. Add 1 teaspoon oil and grind further into a smooth paste.
Heat 1 tablespoon oil in a deep non-stick pan. Add onion, ground paste and sauté for 2-3 minutes.
Add potato, 2 cups water, stir to mix and bring to a boil. Add sweetcorn, half the corn kernels, mix well and simmer till the potatoes are done.
Transfer the cooked mixture into a blender jar and blend into a puree. Transfer the puree in a non-stick pan.
Adjust consistency by using sufficient water and add salt. Mix well and bring to a boil.
Place remaining corn kernels in a serving bowl. Pour soup over it and garnish with some more corn kernels on top. Serve hot.