Cover a baking sheet with tin foil, and put your pan in a 450 degree oven for 10 minutes (just the pan). While the pan is heating up, peel and chop your sweet potatoes into large chunks.

Put the potatoes into a gallon-sized ziplock bag and toss with the other ingredients until coated evenly. Let sit until your pan has heated for a full 10 minutes.

Remove the hot pan from the oven (close the door after you take the pan out to keep the oven hot) and pour the potatoes from the bag directly onto the pan. Spread evenly and put the pan into the oven. Cook for about 10 minutes, then toss the potatoes gently by shaking the pan. Let the potatoes cook for another 5 minutes and check them. If you aren't seeing any dark spots, kick the broiler on high and watch them closely until they begin developing small dark spots, and remove them from the oven. During this process, make the dressing.

For the Dressing: In a small pan, melt your butter and bacon fat (with drippings) together. Once that is bubbling a bit, add the syrup and swirl the pan to get it all mixed in. Add your nutmeg and cinnamon, and swirl it all up again. Let that come to a boil and add your cider vinegar. Swirl the pan some more and get it all incorporated in. Bring it to a simmer and reduce to about 3/4 its volume.

Once the dressing and potatoes are done, carefully put the potatoes into a bowl, add the dressing, and mix VERY CAREFULLY. Here's the thing, even though we roasted at a high temp, soft sweet potatoes are still naturally soft (hence the name). If you get all aggressive with mixing the potatoes up, they'll be all mashed and not appetizing. So take your time, use a thin spoon (using something thick like a wooden spoon won't be able to get under the potatoes as easily, and will end up mashing them more then just using a big soup spoon or something), and even try transferring the potatoes from one bowl to another, back and forth. Serve warm.