Fill a medium-sized pot with water. Add the diced potatoes and bring to a boil over medium-high heat. Boil until the potatoes are very tender, about 20 minutes.

Meanwhile, melt 1 tablespoon of the butter in a large skillet over medium heat. Add the chopped leeks and kale and saute until tender, about 10 minutes. About halfway through the cooking time, add a bit of water (about 2 Tbsp) to prevent the pan from getting too dry and to help steam the veggies.

Once the potatoes are done, strain the pot and return the potatoes either to the pot or to the mixing bowl of your standing mixer. Add the warm milk, the remaining 1 Tbsp of butter, and the sour cream to your hot potatoes. Using either a hand mixer or the paddle attachment on your stand mixer, slowly begin to beat the potatoes until creamy and smooth.

Once the potatoes are mashed, fold in the sauteed leeks and kale plus the salt and pepper. Have a taste and adjust to seasoning to your liking. Serve hot and enjoy!