Put the potatoes in a large pot, cover them with cold water just to the top, and season the water generously with kosher salt. The cold start helps the potatoes cook evenly, and salted water seasons them from the inside.

Bring the pot to a boil uncovered and cook until the potatoes are fully tender. They are ready when a fork, paring knife, or cake tester slides in with no resistance.

Drain the potatoes well in a colander or large sieve. Well-drained potatoes make a creamier mash and keep extra water from thinning the mixture.

While the potatoes cook, prepare the bacon in a sauté pan or on a wire rack set inside a rimmed baking sheet in the oven until browned and crisp. When most of the fat has rendered, move the bacon to paper towels, let it cool, then crumble it.

Transfer the hot drained potatoes to the bowl of a stand mixer fitted with the paddle attachment and mix on low until smooth. If you do not have a stand mixer, mash by hand with a wooden spoon or potato masher until the texture is even.

Add all the butter to the hot potatoes and mix until it is fully melted and absorbed. At this stage the potatoes may look a little dry and fluffy, which is exactly what you want before adding the rest.

Take the bowl off the mixer, stir in the cheddar until melted, then mix in the sour cream, chives, and crumbled bacon. The heat from the potatoes should melt the cheese smoothly and bring everything together into a creamy, savory mash.

If the potatoes become too loose, stir in a small amount of potato flakes to thicken them. The texture changes slightly, but it can bring the mash back together in a pinch.

Finish with kosher salt and black pepper to taste. The final mash should taste rich, cheesy, and well-seasoned with little pops of bacon and fresh chive.