Mix flour, yeast, salt and water for 7 minutes until dough is smooth and stiff.
Fry onions and salt in oil over high heat until onions are dark golden brown with charred bits. Transfer to a bowl to cool.
Bulk ferment dough for 90 minutes, until it has doubled in size.
Gently degas dough and divide into 2.8-oz. pieces. Shape into 4-in. to 5-in. circles, each with a small rim.
Place bialys on prepared baking sheets, and snip a 1-in. hole in the bottom of each bialy.
Evenly spread filling into the center of each bialy, inside the rim.
Cover bialys with parchment paper, then with another baking sheet.
Bake at 450ºF for 4 minutes; remove the top baking sheet.
Bake for another 7 minutes, until golden brown. Cool on a rack.
Yield: about 106 large bialys