Preheat your oven to 350 degrees.
Place the potato directly on the oven rack.
Bake for about 1 hour or until the potatoes can be pierced with a fork.
Carefully pop open the potatoes to allow steam to escape and allow to cool until you can safely handle them.
Warm up your milk or cream in a saucepan. Just warm it through,don't let it boil.
When potatoes are cool enough to handle, scoop out all the potatoes into a bowl.
If you have a ricer, run the potatoes through it.
Add the butter and start with 1/4 cup of the dairy.
Whip with a hand mixer for 10 to 15 seconds to just smooth the potatoes out. Add more dairy if necessary.
Add kosher salt to taste.