Pickled French Fries

Combine 5 tablespoons salt and 8 cups water in a large bowl or pot, stirring until salt dissolves. Add potatoes and cabbage (potatoes should sink, but some of the cabbage leaves may float). Cover bowl and store in a cool, dark place (a kitchen cabinet or pantry is ideal) 4–6 days; the longer the potatoes sit, the funkier their flavor will be. Drain and pat potatoes dry; discard cabbage leaves.
Fit a large pot with thermometer and pour in oil to measure 3" up sides of pot. Heat oil over medium-high until thermometer registers 325°F. Working in batches (you want potatoes to have room to move around), fry potatoes until cooked through and tender but not browned, about 5 minutes. Using a spider or a slotted spoon, transfer fries to paper towels to drain as they are done.
Heat oil until thermometer registers 375°F. Working in batches again, refry potatoes until crisp (the edges may brown, but fries will mostly stay pretty light), about 1 minute per batch. Transfer to fresh paper towels to drain; sprinkle with salt (because of the brine, you won't need to add much).