1. Following manufacturers directions, add buttermilk and water to bread machine. Top with bread flour, all-purpose flour, sugar and salt. Make a well with back of spoon in center of dry ingredients, without breaking through to liquid. Add yeast to well, being careful it does not come into contact with liquid. Close lid of the machine.
2. Set bread machine on dough setting. Begin the cycle. When the cycle is finished, remove the dough to a lightly floured surface. Punch the dough down lightly; let rest for 5 minutes.
3. Coat two 8-1/2 x 4-1/2 x 2-1/2-inch loaf pans with nonstick cooking spray. Divide the dough in half. Roll out each half of dough into a 8-inch square. Roll each square up, jelly-roll fashion. Tuck ends under; place each, seam side down, in one of the prepared pans.
4. Toss together the sesame seeds, poppy seeds, salt and minced onion in a small bowl. Brush the tops of the loaves evenly with the egg white; sprinkle evenly with the seed mixture. Cover the loaves with plastic wrap and a clean kitchen towel; let rise in warm place for about 1 hour, until almost doubled.
5. Heat the oven to 375 degrees F. Uncover the loaves. Bake in the 375 degrees F oven for 25 to 30 minutes or until the tops are browned and the breads sounds hollow when tapped with your fingertips. Remove the loaves immediately from the pans to a wire rack. Let cool completely.To make by hand:
6. Sprinkle the rapid-rise yeast over 2/3 cup warm water (105 degrees F to 110 degrees F) in a small measuring cup. Let stand for 5 minutes or until the mixture is foamy. Stir to dissolve the yeast. Whisk together the bread flour, all-purpose flour, sugar and salt in a large bowl. Make a well in the center of the dry ingredients with the back of a spoon. Add the yeast mixture and the buttermilk to the well. Stir the liquid ingredients into the dry ingredients until a dough forms. Scrape the dough out onto a lightly floured work surface. Knead the dough until smooth and elastic, about 10 minutes, adding more bread flour as needed to prevent the dough from sticking. Place the dough in a greased bowl; turn to coat the dough evenly. Cover with plastic wrap and then a clean kitchen towel; let the dough rise in warm place, about 1 hour, until almost doubled. Punch the dough down lightly; let rest for 5 minutes. Then proceed with Step 3.