St. Patrick's Colcannon

Place potatoes in a large saucepan and add water to cover by 1-inch. Bring to a boil over high heat, then reduce heat to medium-low, cover, and simmer until tender, about 20 minutes. Meanwhile, bring a large pot of salted water to a boil. Stir in cabbage along with 2 tablespoons of butter; cover, and simmer until the cabbage has softened. Drain. Melt 1/2-cup butter over medium heat. Stir in garlic and the white parts of the green onions. Cook until the garlic has softened and mellowed. Drain the potatoes and mash with white pepper to taste. Fold in melted butter, milk, cabbage, and corned beef. Sprinkle with green onion tops to serve.