Add potatoes to a large pot, large enough to hold all of the potatoes and cover with water by about an inch making sure to salt the water (it should be salty like the sea).
Bring potatoes to a boil on high, then reduce to medium and cook for about 20-25 minutes, until a paring knife can be inserted into potatoes with ease.
While potatoes are cooking bring butter, garlic powder, stock to a simmer in a small saucepan.
Drain potatoes and add back to a large pot.
Add parmesan and pepper to potatoes and mush them in for about a minute.
Pour in the warm stock mixture until it is the consistency you like.
You may or may not need the salt at the end depending on the stock, butter, and parmesan. Add to taste.