Combine the potato chunks in a 4-quart saucepan. Add 1 teaspoon of the salt and just enough water to submerge the potatoes.Cover the pot with its lid and bring to a boil over high heat. As soon as steam starts to puff out around the lid, remove the lid and reduce the heat to maintain a simmer, cooking until the potatoes are easily crushed with tongs, about 8 minutes.
Meanwhile melt the butter in an 11-inch straight-sided sauté pan over medium-low heat. Cook, gently shaking the pan, until the butter just starts to brown, 3-4 minutes, then carefully pour half into a heat-proof bowl or measuring cup and set aside.
Increase the heat to medium and add the cabbage along with another teaspoon of the salt and 1/2 teaspoon of the pepper. Sauté, scraping and incorporating the browned bits into the cabbage for about 7 minutes, until it's softened and lightly browned.
While the cabbage cooks, don't forget to check the potatoes. When they're done, drain then return to the pot while it's still hot. Give the pot a few shakes to break up and dry the potatoes, then set aside on a kitchen towel or trivet. Add the warmed milk, remaining 2 teaspoons salt, and remaining pepper and mash to desired consistency with desired utensil.
When the cabbage is lightly brown, add the mashed potatoes to the sauté pan, kill the heat, and combine with a wooden spoon or rubber spatula.
Place the colcannon in a serving vessel of your choice and use the back of a spoon to create a divot in the top of the mixture. Pour the reserved brown butter into said divot and serve immediately to a thankful planet populated entirely by Irishmen.
Oh, and drink the whiskey.