I don't want to tell you how to make mashed potatoes. It seems like one of those things that you just... do. But I still know people to this day who think that mashed potatoes come out of a bag! And classics got that way because they are staples. But sometimes, the quick and easy rehydrated and reconstituted astronaut food in bags aren't actually that much quicker or easier than making them from scratch! And certainly not nearly as delicious. So, indulge a little and take that extra 15 minutes to peel and boil potatoes!
Peel and dice potatoes. They should be able an inch thick.
Place in a large pot and cover with 2 inches of water.
Bring to a boil over high heat.
Boil for 10-15 minutes, or until tender. You should be able to stick a fork in them and have it break in two pieces. They're not quite cooked if the fork comes out cleanly. And they're overdone if it breaks apart completely, instead of just in half.
Drain and place back in the pot.
Add the milk, butter, salt, and pepper.
Mash with a potato masher until light and fluffy. Making sure to scrape the sides and stir occasionally.