Nutrition per serving may change if servings are adjusted.
1½ cups lukewarm water
2 tablespoons active dry yeast
5 teaspoons sugar
4-5 cups bread flour, preferably unbleached
1 tablespoon kosher salt, plus more for sprinkling
1-2 tablespoons cornmeal, for sprinkling baking sheets
1 cup finely chopped onion
1½ tablespoons poppy seeds
1 tablespoon canola oil
1 large egg
2 tablespoons water
Whisk together lukewarm water, yeast and sugar in a large bowl until the yeast dissolves. Stir in 1 cup flour. Stir in salt and enough additional flour to make a soft dough, about 2½ cups.
Turn the dough out onto a lightly floured surface and knead, gradually incorporating more flour as needed to prevent sticking, until the dough is smooth and elastic, 8 to 10 minutes. Cover the dough with a clean dish towel and let rise for 45 minutes.
Meanwhile, line 2 baking sheets with parchment paper, lightly sprinkle with cornmeal and set aside.
Stir together onion, poppy seeds and oil in a small bowl and set aside. Whisk the egg and 2 tablespoons water together in another small bowl.
When the dough has risen, punch it down and divide it into 12 equal pieces; cover and let rest for 10 minutes. Roll or stretch each piece into a 4- to 5-inch oval and place on the prepared baking sheets.
Brush each bialy with the egg-and-water mixture and sprinkle with a heaping tablespoon of the onion-poppy-seed mixture and some salt. Cover with a floured dish towel and let rise until they appear puffy, 30 to 40 minutes.
Preheat oven to 450°F. Place the bialys in the oven, reduce the heat to 425°F and bake until golden brown, 20 to 25 minutes.