Fill a large pot with generously salted water. Add potato slices; bring to a boil. Simmer until the potatoes are tender; drain. Return potatoes to the pot off of the heat; cover with a clean dish towel and allow to sit for 5 minutes (this helps dry out the potatoes, resulting in a fluffier mash).
In a large skillet, melt 2 Tablespoons butter over medium heat. Add chopped kale and cook for about 10 minutes, or until it has softened and turned a vibrant green. Remove from heat and set aside.
In a small saucepan, add milk and remaining 1/2 cup butter; heat over medium heat until butter is melted. Mash the potatoes or press them through a ricer. Pour in hot milk mixture and whip until potatoes are fluffy and light. Stir in cooked kale and salt and pepper, to taste. Transfer to serving bowl; make a well in the top and add a pat of butter.