1. Prepare the Dough: In a large mixing bowl, combine the active sourdough starter, warm water, granulated sugar, and salt. Stir until the starter is mostly dissolved. Gradually add the bread flour, mixing with a wooden spoon or your hands until a shaggy dough forms. Turn the dough out onto a lightly floured surface and knead for 8-10 minutes, until it’s smooth and elastic. It should spring back when poked.

2. First Rise (Bulk Fermentation): Place the kneaded dough into a lightly oiled bowl, turning it once to coat. Cover the bowl with plastic wrap or a damp towel and let it rise at room temperature for 2-3 hours, or until it has visibly increased in size. For a more developed flavor, you can place it in the refrigerator for 8-12 hours (or overnight) after the initial room temperature rise. This slow fermentation enhances the sourdough tang.

3. Shape the Bagels: Gently turn the dough out onto a lightly floured surface. Divide the dough into 8-10 equal pieces (about 4-5 ounces each). Roll each piece into a smooth ball. To create the hole, poke your thumb through the center of each ball and gently stretch the dough to form a 1-inch hole. Aim for an even thickness around the hole. Place the shaped bagels on a parchment-lined baking sheet.

4. Second Rise (Proofing): Cover the shaped bagels loosely with plastic wrap or a damp towel and let them proof at room temperature for 30-60 minutes, or until they look slightly puffy. To test if they’re ready, perform the “float test”: drop one bagel into a bowl of water. If it floats within 10 seconds, it’s ready. If not, let them proof for another 15-30 minutes and retest.

5. Boil the Bagels: Preheat your oven to 425 F (220 C). Bring a large pot of water to a rolling boil and add the baking soda. This alkaline water helps create the chewy crust. Carefully drop 2-3 bagels into the boiling water at a time, making sure not to overcrowd the pot. Boil for 30 seconds to 1 minute per side. Use a slotted spoon to remove the bagels and place them back on the parchment-lined baking sheet.

6. Apply Topping and Bake: In a small bowl, combine the 1/4 cup granulated sugar and 2 teaspoons ground cinnamon for the topping. Brush the boiled bagels generously with the beaten egg white. Immediately sprinkle the cinnamon sugar mixture over the tops of the bagels, pressing gently to adhere. Bake for 18-22 minutes, or until the bagels are golden brown and cooked through. Let them cool slightly on a wire rack before serving.