Peel and quarter the potatoes. Place them in a Dutch oven and cover with cold water. Add salt and bring to a boil. Cook until fork-tender (about 20 minutes).

Once cooked, drain the potatoes and let them sit in the colander to steam off excess moisture.

In a skillet, melt butter over medium heat. Add leeks and green cabbage. Sauté until softened (5-7 minutes). Add garlic and green onions for 2 more minutes.

Pour in the milk, heating gently. Fold in the drained potatoes, mashing lightly into the greens. Adjust seasoning with salt and pepper.

Transfer the Colcannon to a serving bowl. Add a pat of butter in the center and garnish with chives and black pepper.