Place potatoes in a large pot and cover with cold salted water. Bring to a boil and cook 15–18 minutes, until fork-tender. Drain well and let steam dry for a few minutes.

While potatoes cook, heat a large skillet over medium heat. Add chopped bacon and cook until crisp. Remove with a slotted spoon and set aside, leaving about 1 tablespoon of bacon fat in the pan.

Add butter to the bacon fat. Stir in diced onion and sliced leeks. Cook 4–5 minutes until soft and lightly golden. Add shredded cabbage or greens and cook 3–5 minutes, until wilted and tender but still vibrant. Season lightly with salt and pepper.

Mash the hot potatoes with warmed milk, salt, and pepper until creamy but still slightly rustic (colcannon shouldn’t be completely smooth).

Fold in the sautéed greens mixture and most of the crispy bacon. Taste and adjust seasoning.

Spoon into a serving bowl, make a small well in the center, and add a pat of butter to melt. Sprinkle remaining bacon over top. Enjoy!