In the bowl of a stand mixer mix together the sponge ingredients until uniform, cover and let rest for 3 hours.
Add all of the dough ingredients to the sponge except the butter, add a hook attachment and turn on the mixer. Once the dough has formed into a ball add the softened butter and continue to knead for 8 minutes. Cover the dough and let rest in a warm spot for 1 hour.
Turn out the dough onto a floured surface and divide the dough into 6 or 12 pieces. Shape the pieces into elongated ovals and place on greased baking trays, cover and let rest for 1 hour.
Preheat the oven to 375F before the rising time has finished. Bake at 375 for 10-15 minutes depending on the size of your buns.
Let the buns cool completely, make a shallow incision along the top of the bun, spread some mayo into the incision and then slather the top with a generous amount of may, not enough that it drips off. Spread the pork floss on a plate and press the mayo side of the bread into the floss, pack a little more on and tap off some the excess.