Add the potatoes to a large pot and cover with water by 1 inch. Add 3 teaspoons kosher salt and bring to a boil. Boil for 30 minutes or until the potatoes are fork-tender. Turn off the heat.
Drain the potatoes and return them to the warm pot. Place the pot back on the warm burner, leave the heat off, and let the excess water evaporate for 5 minutes.
Mash the potatoes:
Add the garlic powder, white pepper, nutmeg, and butter to the potatoes. Add half the milk. Turn the heat to low. With a potato masher, begin mashing the potatoes to incorporate the butter into the potatoes.
Tilt the pot toward you and continue adding the rest of the milk in increments until the potatoes reach your desired consistency. You may not use all the milk or you may wish to add a few additional splashes if needed.
Taste the potatoes. Add the remaining 1 teaspoon of kosher salt. If desired, add more salt, garlic powder, white pepper, or nutmeg.
To serve:
Spoon the potatoes onto a serving platter and smooth them out, creating divots with the back of your spoon. Enjoy!