The first steps are a lot like mashed potatoes. Pick quantity depending on how many people you're serving -- but use at least five yams or the souffle dish won't be full enough to puff.
Cut the yams and boil them (with their skins on), it's really easier to peel them after they're cooked. Drain in a colander, let cool a tiny bit and peel the skins off.
Mash in a bowl with as much butter and milk as you like until the consistency is slightly creamier than mashed potatoes. Add a tiny bit of salt and freshly ground pepper as you mash.
Separate four eggs, discard the yolks and, in a separate bowl, beat the whites until they're stiff. (Tip: Adding a little salt, makes it easier to beat the egg whites stiff.)
Gently fold the stiff egg whites into the mashed yams.
Pour into a souffle dish.
And bake at 375° for twenty to thirty minutes -- until the souffle rises a bit and there are little wisps of brown at the top. (Use the interior oven light and try not to open the oven until they're done, but it's not quite as delicate as a regular souffle, so it's not disastrous if you do...)
Variations -- if you're looking for something a little spicy, or sultry, or smoky, finely dice one chipotle pepper and add it in as you're mashing the potatoes. Or conversely, add a little nutmeg, (or cinnamon), little being the operative word, before you mash.
And in an effort to be bi-partisan, did I mention this is also excellent if you make it with sweet potatoes instead of yams, a little more subtle and a tiny bit paler, but still delicious.
If you've invented anything for Thanksgiving, we'd love to hear about it!