Place potatoes in a large saucepan filled with enough water to cover potatoes by 1". Heat over high heat until boiling then reduce to simmer. Add 1 tsp of kosher salt and stir. Simmer until potatoes are very tender but not disintegrating (about 20 minutes). Drain potatoes completely and return to pot.

Stir potatoes over low heat to allow excess water to evaporate—potatoes should break down easily just from stirring (the process is complete when no steam rises from the pot—approx. 1 minute).

Transfer potatoes to a large mixing bowl or the bowl of a stand mixer fitted with the whip attachment. Begin beating potatoes on low speed, gradually working up to medium speed to break down any lumps. Add butter, beat on medium speed until fully, scraping down the sides of the bowl often.

Add half-and-half or milk and 1 cup shredded cheddar cheese and beat on medium speed until potatoes are light and fluffy.

Sprinkle potatoes with 1 tsp kosher salt and whip on high speed an additional 20 seconds.

Let potatoes sit 2 minutes then fold in remaining cheese. Season with pepper to taste.

Transfer to a serving dish and enjoy!