Dissolve the salt and brown sugar in 1/4 cup warm water. Pour into a large resealable plastic bag with remaining 2 3/4 cups water. Place pork in bag, seal and refrigerate overnight.
In a small microwavable bowl combine peanut butter, sake, soy sauce, vinegar, honey, peanut oil, chilli paste, chilli sauce, garlic, ginger, spring onions and coriander. Microwave for 30 seconds to 1 minute to melt peanut butter; mix thoroughly.
Reserve 1/2 to 3/4 cup of this peanut sauce to serve as a sauce for the cooked meat; refrigerate until ready to use. Pour remaining sauce into a resealable plastic bag. Remove pork from brine; discard brine. Rinse pork, pat dry and place in the bag with the peanut sauce marinade. Refrigerate for 8 hours, or overnight.
Preheat barbecue for medium heat. Take pork out of peanut sauce marinade; let sit at room temperature for about 20 minutes. Pour marinade in small saucepan. Heat to a boil and boil for 3 minutes. If marinade gets too thick add a little milk to thin.
Lightly grate and arrange tenderloins on barbecue. Baste pork two or three times, watching carefully after basting so that it doesn't burn. Cook about 15 minutes. Pull off the barbecue and let sit for 5 minutes before slicing into thin rounds.
Warm the reserved sauce in the microwave and place a dollop of the sauce on each plate. Place pork slices on top of sauce to serve.