A classic, catered to your tastes.
2 pounds potatoes (we prefer Yukon Gold)
1/2 stick to 1 stick (1/4 cup to 1/2 cup) unsalted butter, at room temperature
1/2 cup to 1 cup liquid, warmed (see discussion below)
salt and pepper to taste
1. Place whole potatoes in a large pot of boiling, salted water. Boil until tender, 20 to 40 minutes, depending on size of potatoes.
2. When cool enough to handle, rice potatoes in a potato ricer (if you're using another mashing device, you'll have to peel the potatoes first).
3. Place the riced potatoes back in the pot over moderate heat. Stir for a few minutes, until potatoes are warm and dry. (Make sure not to burn them.)
4. Beat in the butter. Beat in the warmed liquid. Whisk vigorously until potatoes are lightened (about a minute with a hand-held whisk). Season to taste with salt and pepper and serve immediately.
Here's an all-purpose mashed potato recipe -- but the specific liquid and the amounts of liquid and butter are up to you, depending on how thick/thin, buttery/nonbuttery you like your mashed potatoes. Serves 4 as a side dish.