Cook up 4 slices of bacon. While it cooks, wash and slice a large sweet potato on the mandolin. Cut the chard stems out of the chard (about 2 bunches) and cut crosswise to produce 1/4″ thick slices.
Remove the bacon when browned and put the sweet potato slices and chard stems in the hot fat, cook on medium for about 10 minutes. Meanwhile, cut the chard leaves into ribbons.
Mix up the white sauce in a bowl. The white sauce is 1 can of cream of mushroom soup, 1 cup of sour cream, and 1 cup of shredded jack cheese.
Butter the bottom and sides of a 13×9 casserole dish. Transfer the sweet potato & stems into the bottom on the 13×9; it creates a sparse layer. Add butter or bacon fat (maybe 3 tbsp.) to the stovetop pan. When it melts, add the chard leaves, stir for about 2 minutes, remove. Layer about 1/2 of the wilted leaves over the sweet potatoes. Add the white sauce, top with the remaining chard and bacon, and cover with one more cup of jack cheese.
Bake @ 350 for 30 minutes; remove and serve.