Peal and cut up the potatoes into medium chunks. Mine were about 1 inches cubed but there is no need for perfection here…you are going to mash them! Place potatoes in a medium sauce pot and cover with cold water. Bring to a boil over medium-high heat and then reduce heat to medium to maintain a slow boil.
Cook until the break apart easily with a fork. They should be very tender! The time will vary greatly by how large your pieces are! Mine took about 20 minutes.
While your potatoes cook, heat your butter in a small saucepot or skillet over medium heat, swirling occasionally until the butter turns a golden brown and it takes on a nutty aroma. There are only a few moments between perfect and burned, so watch it like caramel!
Remove the butter from the heat and stir in sage, it will boil. Gently swirl the sage in the butter until it stops bubbling and set aside until your potatoes are ready. If you wait too long and your butter starts to reharden, you can just heat it gently over low heat until it is liquid again.
Drain the potatoes and either mash with the back of a wooden spoon or press through a ricer (my favorite option). Give the potatoes a good stir with the wooden spoon before pouring in about half of you sage butter. Make sure that you get sage with the butter. Add a large pinch of kosher salt and a few grinds of black pepper. Beat well, taste and add more sage butter and salt as needed. I used about ¾ of my butter and all of the sage (just pull it out of the butter with a spoon) in my mashed potatoes, and then drizzled a little extra brown butter on the top to finish it.