Preparation Pulse kosher salt and fennel in grinder until fennel is coarsely ground. Arrange fatback, skin side up, on a work surface with longest side nearest you. Score pork skin (1/4 inch deep) crosswise with a sharp knife at 1/3-inch intervals (do not cut through to fat). Pat skin completely dry with paper towels, then rub fennel salt into skin. Let stand, loosely covered, at room temperature 1 hour. Put oven rack in bottom third of oven and preheat oven to 450°F. Pat skin completely dry with paper towels again, then cut skin into strips using scored cuts as a guide. Arrange strips close together in a large shallow baking pan (1 inch deep) and slowly pour water into pan (not over skin). Roast, stirring twice (use caution, as fat may splatter), until strips are golden, blistered, and crisp, 30 to 35 minutes. Transfer with a slotted spoon to a paper-towel-lined plate to drain, then discard fat remaining in pan. Cooks' note:Cracklings can be made 6 hours ahead and cooled, uncovered, then kept, covered, at room temperature. Reheat in upper third of a preheated 425°F oven until hot, about 10 minutes.
Preparation Pulse kosher salt and fennel in grinder until fennel is coarsely ground. Arrange fatback, skin side up, on a work surface with longest side nearest you. Score pork skin (1/4 inch deep) crosswise with a sharp knife at 1/3-inch intervals (do not cut through to fat). Pat skin completely dry with paper towels, then rub fennel salt into skin. Let stand, loosely covered, at room temperature 1 hour. Put oven rack in bottom third of oven and preheat oven to 450°F. Pat skin completely dry with paper towels again, then cut skin into strips using scored cuts as a guide. Arrange strips close together in a large shallow baking pan (1 inch deep) and slowly pour water into pan (not over skin). Roast, stirring twice (use caution, as fat may splatter), until strips are golden, blistered, and crisp, 30 to 35 minutes. Transfer with a slotted spoon to a paper-towel-lined plate to drain, then discard fat remaining in pan. Cooks' note:Cracklings can be made 6 hours ahead and cooled, uncovered, then kept, covered, at room temperature. Reheat in upper third of a preheated 425°F oven until hot, about 10 minutes.