Pop the potatoes into a medium saucepan and fill with cold water until covered by about 1-inch. Season well with salt. Bring to a boil, lower to a simmer, and cook until a fork inserted into the center of the potato meets no resistance, 20 to 30 minutes. Drain and pass through a ricer or food mill. Stir in the butter while hot.
Warm the oil over medium-high heat in a skillet, preferably cast iron. Add the seeds; they should sizzle upon contact. Once they stop popping, add the onions and saute until softened.
Add the mashed potatoes to the pan and flatten with a spatula so that potatoes can begin to crisp. Continue to toss and re-flatten the potatoes until there are patches of crispy deliciousness all the way through the potatoes, about 10 minutes. Remove from the heat, sprinkle with parsley, and serve.
Recipe courtesy of Aarti Sequeira