Serves 4 INGREDIENTS 3 tablespoons canola oil 1 teaspoon nigella seeds (optional) 1 teaspoon cumin seeds Rounded ¼ teaspoon coriander seeds A 2-inch piece fresh ginger, peeled and chopped 1½ pounds red boiling potatoes, peeled, halved, and sliced lengthwise about ½ inch thick 1 small to medium head cauliflower, cored and cut into medium florets…