In a medium cast-iron skillet, sauté shallots over medium heat until golden and translucent, 5-7 minutes. Add the sliced garlic and sauté until golden on both sides, another 3-5 minutes. Transfer to a mixing bowl.

Boil potatoes until very tender when pierced with a thin sharp knife. Drain in a colander. Use a potato ricer and press through still-warm potatoes into bowl with shallot mixture, adding 3/4 the butter in small pats between rounds so it melts while you work.

Sauté cabbage over same heat as you did the shallots and garlic, and after a few minutes, add a splash of water to help soften it further. Cabbage should be soft and translucent once ready, about 7—10 minutes in all.

Add cabbage and milk to the potato mixture and fold in with a spatula until well combined. Generously season with salt and pepper and taste. Adjust as needed. Swirl colcannon mash into bowls, top with more butter, and eat at once.