Sift both flours into the mixing bowl of an electric mixer fitted with a dough hook. Add salt, sugar and milk powder, then beat for 10-20 seconds. Stir in yeast and egg, then pour in water gradually. Mix into a dough. Add butter and knead into a smooth and pliable dough.
Remove dough to a lightly greased bowl. Cover with a damp tea towel and set aside to proof for 30-40 minutes or until doubled in size.
Remove dough to a lightly floured table top. Scale the dough to portions of about 75g each and shape each piece into an oval. Put the shaped dough on greased trays, spacing them well apart. Leave to rest for 25-30 minutes to allow the dough to rise again.
Brush the buns with glaze and bake in a preheated oven at 180°C for about 15 minutes.
Cool the buns on a wire rack. Use a serrated bread knife and cut the buns open. Spread with a little mayonnaise. Replace the tops and brush a thin layer of mayonnaise on the top. Sprinkle chicken floss.