Method
Put the potatoes in a soup pot (basically something that is wide enough to saute the greens but also big enough to boil the potatoes) and cover with cold water by at least an inch. Generously salt. Boil until the potatoes are fork tender, 15 to 20 minutes. Drain potatoes in a colander.
Heat the butter in the soup pot over medium heat. Add in the onions and saute for a few minutes until translucent and fragrant. Add chopped kale and cook until wilted and bright green, about 3-4 minutes. Season with salt. Pour in milk or cream and the Roasted Garlic Achaar and mix well.
Next add in the boiled potatoes. Start mashing and stirring the potatoes and greens together. It will seem soupy but continue to mash and cook until you get to a nice creamy texture. Taste and adjust for salt, butter and Roasted Garlic Achaar.
Transfer to a serving bowl. Top with pats of butter and Roasted Garlic Achaar as needed. Serve warm.