Add potatoes, garlic, and salt to a large pot of cold water. Cover and bring to a boil, then reduce heat and simmer for 20–25 minutes.

Heat milk and oil in a small pot over medium heat. Stir until combined. Remove from heat and set aside.

Drain the potatoes and garlic before returning to pot. Stir over low heat for 1–2 minutes, until remaining water evaporates.

Transfer potatoes and garlic to large bowl. Mash or mix potatoes and garlic, stirring in milk mixture slowly as you mash, until desired texture.