Mix the tomato paste, water, cayenne, turmeric, ground coriander, ground cumin, garam masala and amchur or lemon juice in a bowl. Set aside.
Make aloo gobi
Heat the oil in a skillet or wok. Add the cumin seeds. As they begin to turn a little darker and fragrant, add the onions with the jalapeno and ginger garlic paste. Add some salt. Sauté over medium heat until the onions soften and become translucent, which should take 3-4 minutes.
Add the potatoes and cauliflower to the pan and toss to mix with the onions. Cover the pan with a tight lid and turn heat to low. Stir the potatoes and cauliflower occasionally to ensure they don't stick to the bottom of the pan. If they do, add one or two tablespoons of water and continue to cook until the vegetables are tender, about 10 minutes.
Pour the reserved sauce over the cauliflower and potatoes and gently mix, taking care not to break the cauliflower florets. Cover the pan and cook on low heat for two minutes so the spices in the sauce cook through.
Check and add more salt if needed to the aloo gobi. Garnish with cilantro and serve hot.
Notes
Separate the cauliflower in large florets because the cauliflower will break into smaller florets on its own after cooking. This will also ensure that the cauliflower cooks at the same time as the potatoes and doesn't get mushy.
Ingredient notes:
Tomato paste: Using tomato paste instead of tomatoes ensures the dish has more umami and flavor. It also cuts down on cooking time significantly than if you were using tomatoes or tomato puree.
Amchur: Amchur or dried mango powder is optional in this recipe and you can skip it if you use the lemon juice. It has a more complex tartness, with an undertone of sweetness.