-As many potatoes as you want. At our house, it's not unusual for me to do a 10 lb bag and cook it all. But really about a dozen nice sized potatoes will make a large bowl of mashed potatoes, plenty for dinner for 4 or 5 people.
-Butter - 1 or 2 sticks depending on how much you're cooking
-Salt and Pepper to taste
You can use any kind of potatoes really, I've used plain old russet, red skins or even lovely new potatoes. My favorite at the moment is the Yukon Gold type. They have a nice buttery flavor on their own so you don't need to add as much butter.
In a large stock or soup pot, filled about 3/4 with water, add salt and bring to a boil. While you're waiting for the water to boil, wash and peel the potatoes. I usually just drop them in as I go, the water doesn't have to be boiling first.
Cook over medium to high heat at a boil for about 15 to 20 minutes. Depending on the size of the potatoes. The larger they are, the longer it will take. You can always halve them if they are really large and it will cut down the cooking time.
Once the potatoes are fork tender, but not falling apart, turn off the heat. Drain gently.
In a large mixing bowl, put a stick of butter down and then pour the drained potatoes over the butter. This will help to start the butter melting. If you use a softened stick, all the better.
With a potato masher, start smashing them. You don't want to beat them to death or they'll start to get a gluey texture.
I used to use a hand mixer, but have found the taste and texture is much better with an old fashioned hand masher. Mix as you smash. Once you've broken the potatoes up for the most part, start adding milk. For about 12 potatoes, figure about a cup of milk, but pour it in gradually, mixing in until combined before you add more. The goal is to achieve the consistency that you like. Oh, and don't even try to get all the lumps out, that's what makes them great. We like a few lumps in ours, they add a texture that is wonderful and trying to get them perfectly smooth will turn them into glue.
Add your salt and pepper to taste at this point also, but don't over do it on the salt. You can always salt each persons serving to their taste and potatoes do tend to soak up the salt.
That's it, pretty simple. Now you could add all sorts of things into them, cheese, sour cream, chives, other herbs as you like. That's the great thing about a simple base recipe, it's adaptable.
These potatoes will keep very nicely in the fridge, covered for several days and are perfectly fine heated up in the microwave. My kids and husband love a nice hot gravy on top as well, but for me? Butter and salt are just fine.