Place the milk, water, butter, salt, sugar, onion powder, 2 tablespoons onion flakes, potato flakes, flour and yeast into the pan of a bread machine in the order recommended by the manufacturer. Select the Dough cycle and press Start.
When the cycle has completed, remove the dough from the machine and knead on a lightly floured surface. Cut into 8 equal pieces and form into balls. Gently flatten the balls until they are 10cm in diameter. If they keep shrinking back, just let them relax for a minute before flattening. Place on a baking tray and cover loosely with a towel. Set in a warm place to rise until doubled in size, about 40 minutes.
Preheat the oven to 180 degrees C. Whisk together the egg white and water in a cup. Brush over the tops of the risen rolls, and sprinkle with remaining onion flakes.
Bake for 15 to 20 minutes in the preheated oven until golden brown. Cool completely, then slice in half horizontally before using.