1) To make the dough: Combine all of the dough ingredients, and mix and knead themby hand, mixer, or bread machineto make a soft, somewhat tacky dough.
2) Place the dough in a lightly greased bowl or other container large enough to allow it to at least double in bulk, cover, and let it rise for about 60 to 70 minutes, till it's just about doubled.
3) Transfer the dough to a lightly greased work surface, and pat/roll it into a 12" x 17" rectangle
4) Sprinkle the dough with the minced onion, and press/roll it into the surface gently.
5) Starting with a short (12") end, roll the dough into a log, sealing the ends and side seam.
6) Cut the log into eight slices. A pair of scissors works very well here.
7) Place the buns on a lightly greased or parchment-lined baking sheet, flattening them to about 3" wide. Cover them, and allow them to rise till they're very puffy, about 1 hour. Towards the end of the rising time, preheat the oven to 375°F.
8) Uncover the buns, brush them with the beaten egg white/water, and sprinkle with seeds, if desired.
9) Bake the buns for 20 to 25 minutes, until they're golden brown and feel set when you poke them.
10) Remove them from the oven, and cool on a rack. When completely cool, wrap in plastic, and store at room temperature.