Mix the salt, soy sauce, wine, and five spice powder in a small bowl and massage into the duck. Leave the duck breasts skin side up on a plate uncovered, and let sit in the refrigerator overnight to marinate and to let the skin dry out. (If you don't want to wait overnight, reduce the marinating time to 30 minutes).
Prepare mandarin pancakes:
Mix the flour and salt in a heatproof bowl. Pour the boiling hot water into the flour mixture and use chopsticks or a spatula to mix until a dough ball forms. Once it is cool enough to handle, knead the dough for 8 minutes until smooth, adding flour if the dough is too sticky. Cover with plastic and allow the dough to rest at room temperature for at least 1 hour.
Roll the dough into a cylinder and cut into 12 equal pieces. Form each piece into a dough ball, then flatten them out into a small disc about 2 inches in diameter. Lightly brush 6 of the discs with oil, ensuring the sides of the discs are also brushed with oil. Layer the remaining 6 discs over the 6 oiled discs so you have 6 pieces, each comprised of 2 discs.
Use a rolling pin to roll the discs into 7-inch circles, flipping the pancakes frequently so both of the dough discs are rolled into the same size.
Heat a wok or frying pan over medium low heat, and place one pancake into the pan. After 30 to 45 seconds, you should see air pockets begin to form between the two pancakes. Flip the pancake; it should be white with just a couple of faint brown patches. Any more than that, and they are overcooked. After another 30 seconds, the air pockets should be large enough to separate the two pancakes. Remove the pancake to a plate, and let it cool for another 30 seconds. Now carefully pull apart the two pancakes at the seams. Place finished pancakes onto a plate and cover with a warm kitchen towel. Repeat until all pancakes are done.
The pancakes can be reheated in a steamer for about a minute when ready to serve. They also keep in the freezer for up to 3 weeks if you decide to make a larger batch.
Cook the duck and assemble:
Next, preheat the oven broiler on low heat. Heat an oven-proof pan over medium-high heat, and add 1 tablespoon of oil to coat the pan. Sear the duck breasts, skin side down. Move them frequently so the skin crisps up and fries in the duck fat that renders out. After 8 minutes, or when the duck skin is golden brown and a little bit crispy, carefully drain off the duck fat and discard (or save for later application to other recipes). In the pan, flip the duck breasts (so they are skin side up), and transfer them to the broiler for about 3 minutes. Be careful not to burn the skin, which at this point should be a bit crispy.
Remove the duck from the broiler and let rest for 10 to 15 minutes. The duck will be cooked about medium well and will be very juicy. Transfer to a cutting board and, using a sharp knife, cut into thin slices.
Serve the duck with your warmed pancakes, fixings, and sauce.