1. Combine Wet Ingredients and Starter: In a large mixing bowl, whisk together the active sourdough starter, warm water, granulated sugar, and salt until well combined. The mixture should look slightly milky and bubbly from the starter.

2. Mix in Flour and Blueberries: Gradually add the bread flour, one cup at a time, mixing with a wooden spoon or your hands until a shaggy dough forms. Once most of the flour is incorporated, gently fold in the blueberries and lemon zest. Be careful not to crush the blueberries too much.

3. Knead the Dough: Turn the dough out onto a lightly floured surface. Knead for 8-10 minutes until the dough is smooth, elastic, and no longer sticky. It should pass the “windowpane test” – if you can stretch a small piece of dough thin enough to see light through it without tearing, it’s ready.

4. First Rise (Bulk Fermentation): Place the kneaded dough in a lightly oiled bowl, turning it once to coat. Cover the bowl with plastic wrap or a damp kitchen towel and let it rise at room temperature for 2-3 hours, or until it has visibly increased in size (about 20-30%). Then, transfer the bowl to the refrigerator for a cold proof of 8-12 hours, or overnight. This slow, cold proof develops flavor and makes the dough easier to handle.

5. Shape the Bagels: The next morning (or after the cold proof), gently punch down the dough. Divide it into 8-10 equal pieces (about 100-120g each). Roll each piece into a smooth ball, then use your thumb to poke a hole in the center. Gently stretch the hole to about 1-1.5 inches in diameter, creating the classic bagel shape. Place the shaped bagels on a parchment-lined baking sheet.

6. Boil the Bagels: Preheat your oven to 425 F (220 C). Bring a large pot of water to a rolling boil. Add the baking soda and honey (or maple syrup) to the boiling water. Carefully drop 2-3 bagels into the boiling water at a time, ensuring they don’t overcrowd the pot. Boil for 30 seconds to 1 minute per side. The longer they boil, the chewier the bagel will be.

7. Bake to Golden Perfection: Using a slotted spoon, remove the boiled bagels and place them back on the parchment-lined baking sheet. If desired, sprinkle with your chosen toppings (everything bagel seasoning, poppy seeds, etc.). Bake for 20-25 minutes, or until golden brown and cooked through. Let them cool on a wire rack before slicing and serving.