1.Place potatoes in a large pot and pour in cold water to cover by 1”. Add salt and bring to a boil. Reduce heat and simmer until potatoes are very tender but not saturated or crumbly, 20–25 minutes (boiling will lead to waterlogged pieces).
2.Drain potatoes, reserving ½ cup cooking liquid if making potatoes ahead. Return potatoes to pot and set over low heat. Gently stir until dry, about 1 minute.
3.Meanwhile, heat milk, thyme sprigs, if desired, bay leaves, and ¾ cup butter in a small saucepan over medium heat until butter is melted. Remove from heat.
4.Pass hot potatoes through a ricer into a large bowl (if allowed to cool, the potatoes will become gummy).
5.Remove herbs from warm milk mixture; discard. Gradually add milk mixture to potatoes, stirring vigorously with a wooden spoon until combined and smooth; season with salt and pepper.
6.Serve mashed potatoes with a few pats of butter on top.