Combine the Kosher Salt (2 teaspoon) with Black Peppercorns (1/2 tablespoon), Sage Leaves (1/4 cup), Garlic (4 clove), and Fennel Seeds (1/2 tablespoon) in a spice grinder, or a food processor.
Process until a rough paste is formed, scraping down sides as necessary, about 30 seconds.
Pat Skin-On Turkey Breast (2) dry. Carefully remove the skin from the breast, and lay it flat. Starting with the thicker end of one of the breasts, carefully use a knife to cut through it horizontally, stopping with about 1/2-inch left.
Fold out the breast flat so that it’s now twice as large, and half as thick. Repeat with the second breast. Cut a series of parallel slashes at 1-inch intervals in the turkey meat about 1/2-inch deep. Don't cut all the way through!
Repeat with a second series of slashes perpendicular to the first. Rub the spice/herb mixture into the meat, making sure to get it into all of the cracks.
Carefully roll the turkey meat into a tight cylinder, using the skin to completely enclose it. Tie the roast tightly with butcher's twine at 1-inch intervals, as well as once lengthwise.
Transfer to a sous-vide-style vacuum seal bag. Seal tightly, and let rest for at least 6 hours and up to 2 days.
Preheat sous-vide water bath to 140 degrees F (60 degrees C). Add turkey, and cook for 4 to 5 hours. Remove and run under cool running water, or transfer to an ice bath to chill for five minutes.
Remove from bag, saving any juices, if desired, to make a gravy. Rinse thoroughly, and carefully pat dry with paper towels.
Heat the Peanut Oil (1 1/2 quart) to 400 degrees F (200 degrees C) in a large wok or Dutch oven.
Carefully slide turkey into oil using spatulas and tongs-it will not be fully submerged. Immediately cover and cook, shaking the pan occasionally until sputtering dies a bit, about 2 minutes.
Adjust flame to maintain a 350 degrees F (180 degrees C) temperature. Using a large metal ladle, spoon hot oil over the exposed portions of the roast continuously until the bottom half is cooked and crisp, about 5 minutes.
Carefully flip, and cook on second side. Baste the whole time, until equally golden.
Remove turchetta to a large paper towel-lined plate, and blot all over. Season with salt. Let rest 5 minutes.
Carve, serve, and enjoy!