Place the peeled and cubed Yukon Gold potatoes into a large pot. Cover cool water until submerged. Stir in 1 1/2 tsp of kosher salt.
Simmer over medium heat for around 30 minutes. They are done when fork-tender.
As the potatoes simmer, heat the butter and milk in a small pot or microwave until melted, do not boil.
Once the potatoes are tender, drain them and return to the pot.