Season chicken breasts with kosher salt. Let sit at least 5 minutes. Fill a wide, shallow nonreactive bowl or casserole dish with buttermilk. Add the chicken and soak in the refrigerator for 1 hour up to overnight.
For the vinaigrette: Combine mustard, vinegar and salt in a bowl. Slowly whisk in olive oil until well blended.
For the coleslaw: Macerate onions in the cup of red wine vinegar, and let sit at least 20 minutes. Remove onions and discard vinegar. Toss onions with jalapeno, parsley, cabbage and salt. Toss with vinaigrette until evenly coated.
To fry chicken: Pour vegetable oil into a large stockpot. Do not fill up more than halfway, or the oil could splatter. Bring oil up to 365°, using a digital thermometer/candy thermometer to monitor the heat. Prepare the the breading while waiting for oil to heat up.
In a wide shallow bowl, mix flour, cayenne, salt and pepper. Pull a chicken breast out of the buttermilk one by one, letting excess drip off, and dredge completely in flour. To create a thick crust, place in buttermilk and dredge in flour a second time. Do not drain or shake off excess buttermilk or flour during the breading process.
When the oil is at 365°, carefully place chicken pieces into oil one by one. Let it cook for a minute before disturbing chicken, then help it “swim” in the oil with tongs, until it is evenly cooked, about 5-7 minutes. Remove chicken from oil and drain on paper towels. Season immediately with salt.
For the sandwich: Place fried chicken breast on bottom of torpedo roll and top generously with coleslaw.
Per serving: 995 calories, 52 g protein, 63 g carbohydrate, 58 g fat (8 g saturated), 95 mg cholesterol, 1,497 mg sodium, 6 g fiber.