Peel and cut the Floury Potatoes into even chunks, place them in a large pot of cold water, bring to a gentle boil and simmer until they are easily pierced with a fork (about 15–20 minutes).
While the potatoes cook, shred the Green Cabbage and thinly slice the Spring Onions. Heat a knob of Unsalted Butter in a large skillet over medium heat, add the cabbage and cook, stirring occasionally, until wilted and beginning to caramelize (about 8–10 minutes); stir in the spring onions for the last minute to soften.
When the potatoes are tender, drain them well and return to the warm pot. Mash them until mostly smooth.
Warm the Whole Milk (just until steaming) and stir it into the potatoes a little at a time until you reach a creamy consistency; fold in a generous splash of butter for richness.
Fold the sautéed cabbage and spring onions into the potato mixture gently so the vegetables stay slightly distinct — the result should be a fluffy mash with ribbons of cabbage throughout.
Season the colcannon to taste with Fine Sea Salt and freshly ground Black Pepper, adjusting milk or butter if you prefer it looser or richer.
Serve hot as a side, with an optional pat of butter on top and a few extra chopped spring onions for color.
