Step 1

Combine bread flour, yeast, salt, and water for dough in a bowl. Stir with a wooden spoon and mix until a very wet, soft, and sticky dough forms. Cover and leave at room temperature for at least 12 hours.

Step 2

When ready to make the bialys, heat olive oil for filling in a skillet over medium heat. Add onion and salt and cook, stirring occasionally until onion softens, sweetens, and turns golden brown, about 10 minutes. Turn off the heat and add bread crumbs, 2 teaspoons poppy seeds, green onion, and cayenne pepper. Stir to combine and cool down until needed.

Step 3

Uncover dough; it should be bubbly. Scrape it away from the sides of the bowl with a spatula and transfer onto a floured work surface. Dust a little flour over top and gently press dough with your hands to flatten. Divide it into 8 equal portions and roll each into a ball, using a bit of flour as needed. Stretch each ball gently and tuck dough under the bottom; place on a baking sheet lined with generously floured parchment paper or a silicone liner (such as Silpat®). Dust the tops with flour and carefully cover with a dish towel; let proof until just about doubled in size, 45 to 60 minutes.

Step 4

Preheat the oven to 500 degrees F (260 degrees C).

Step 5

Flour your fingers and pick up one dough ball. Press and pull on the center to form it into a ring shape; the center of the dough will be thin and the edges will be thicker. Make sure the centers are very thin but be careful not to tear them open. Repeat with remaining balls.

Step 6

Fill the center of each with no more than a rounded teaspoon of onion-poppy seed filling, then gently press the filling up the sides toward the outer rings. (You will have extra filling.) Spray bialys with some cold water and sprinkle poppy seeds over top.

Step 7

Bake in the center of the preheated oven until puffed and nicely browned, about 12 minutes. Transfer to a wire rack and cool for about 20 minutes before serving.