Place the potatoes in a large saucepan of lightly salted cold water and bring to the boil. Simmer for 15-20 minutes or until the tip of a knife goes through them easily. Drain well and set aside until cool enough to handle.
Meanwhile, to make the dressing, whisk together the lemon juice, garlic, mayonnaise, sour cream and half the oil, then season to taste. Heat the remaining oil in a small saucepan over low-medium heat, tilting it so the oil collects in one area. When hot, add the mustard and cumin seeds, shake the pan for 2-3 seconds, then add the fennel seeds. Reduce the heat to low and cook for another 10 seconds or until the popping dies down. Remove from the heat and stir into the dressing.
Peel the potatoes, then cut in half if small or quarters if large and place in a large bowl. Add the dressing, red onion, chilli and chaat masala and stir gently to combine well. The potatoes will absorb the dressing as they cool. Just before serving, stir in the radishes, their leaves and the fresh coriander just and adjust the seasoning if necessary.
Serving size: 4
Recipe courtesy of sbs.com.au