3 pounds russet or
Idaho potatoes, peeled and quartered
6 ounces butter (equals 12 tablespoons), cut into chunks, at room temperature
12 ounces half-and-half
Salt and pepper (I prefer white pepper for this), to taste
your oven to 300 degrees (optional; see step 5 below).
2) Place potatoes in a heavy pot, cover them with cold water by an inch, and bring to a boil over high heat. When the water is boiling, add enough salt to make it taste nearly like seawater, and turn the heat down to a moderate simmer. (Starting them in cold water saves time and lets the heat penetrate the potato more evenly.) Cook the potatoes until a paring knife slips in and out of them easily; check them after 15 minutes, then every few minutes thereafter. Even though you're going to mash them to a pulp, it is possible to overcook them — the cells will burst, release starch, and absorb water. How gross does that sound? So be vigilant when they're nearly ready.
3) A few minutes before the potatoes are done, warm the half-and-half in a small pot. Try not to boil it, but you want it nice and steamy. What we're doing is making sure the potatoes stay hot at every step of the way, not just because hot food should be hot, but because this keeps them from turning stiff. When the half-and-half is warm, season it aggressively with salt and pepper — you want it tasting a little bit saltier than is pleasant, because this is going to season the potatoes later.
4) If you're using a food mill, set your colander in the bowl of the mill and drain your potatoes, letting the hot water warm up the mill. (If you're not afraid, you can heat up your potato ricer too, but don't burn yourself on the handle!)
5) Drain the potatoes thoroughly, spread them in one layer on a baking sheet, and put them in the oven to dry. While you're at it, get your mixing or serving bowl nice and hot in the oven, too. Check on the potatoes after 3 minutes or so, and give them a gentle turn. When all the steam has come off and the outsides of the potatoes look floury, they're ready. (Alternatively, you can dry them back in the pot over very low heat, stirring to release the steam, but I like the simplicity and consistency of the oven.) The idea here is to rid the potatoes of all the excess moisture, letting them be as fluffy and light as possible. Well, as fluffy and light as possible when you drench them in butter and cream, anyway.
6) Set the potatoes in the mill or ricer and purée into your hot bowl, alternating every few chunks of potato with some butter; this helps you mix them together evenly. Fold the whole mash a few times with a spatula or spoon, tasting in various spots of the bowl, to make sure the butter is evenly distributed. The butter, on top of being delicious, will coat the cells of the potato and keep the half-and-half from waterlogging them. Science is magic!
7) Pour in the hot half-and-half in a moderate stream, folding or whisking just until it's incorporated. The potatoes should be moist but still firm enough to hold their shape. If they're stiff, add a little more half-and-half. Taste, add salt or pepper if need be, and keep hot! (And try not to eat it all before dinner's ready.)