In a mixing bowl combine flour, yeast, sugar, and salt. Mix 1 minute. Next add water and half of the beaten egg. Mix. Add butter until combined. Knead by hand until smooth and elastic, about 10 minutes.
Cover the dough and let rise in a warm place for about 30 minutes. After that, punch the dough down and make 8 round balls and allow them to rise for 10 minutes .
Now take out each ball and roll out with a rolling pin until you get a thin disk (diameter 5 inch, thickness 1/4 inch).
In a pan heat 1/2 table spoon olive oil over medium high heat add garlic and mix. Next add onion, salmon, and mashed potatoes. Mix until onion is softened and everything is heated through. Add pepper and salt. Mix well.
Now place a tablespoon full of filling mixture in the middle of each disk. Fold the edges of the disk in three places to cover the filling.
Place the fish buns on a greased baking tray and allow to rise for 35 minutes. Next brush the remaining beaten egg over the fish buns and sprinkle some sesame seeds on top.
Bake at 200 C for 20 minutes or until golden brown.