Put the chopped potatoes in a large pot of boiling water. Add a pinch of salt to season. Boil until the potatoes are fork-tender, about 15 minutes. Drain in a colander.
Place a skillet on your stove and heat to medium. Add butter to the skillet. Once melted, add the kale and sauté until wilted, around 3-4 minutes. Then add the green onions.
Put the potatoes back in the large pot and mash them with a masher before adding the kale and green onions.
Add the milk to the pot. Using a spoon, mix the ingredients well, so it becomes smooth. Add 1 teaspoon salt, depending on taste.
Serve with extra butter.