Feed starter the night before. 8 hours before you’re ready to make these bagels, feed your sourdough starter by adding 30 grams of sourdough, 45 grams of flour, and 45 grams of water (this will give you 100 g of active sourdough if you want more to feed later, double this). Stir to combine, cover, and let it sit at room temperature for 8 hours or until it’s doubled in size.
Mix water, honey, and starter. In a large mixing bowl, add the warm water, honey (or sugar), and active sourdough starter. Stir until the water and sourdough starter are almost fully incorporated.
Add salt and flour. Add the salt and flour to the mixing bowl and stir to combine. Use a wooden spoon as much as you can, but you may need to use your hands to add the rest of the flour.
Rise. Form the dough into a ball. Place into a clean bowl and cover with a towel, plate, or plastic wrap. Let it sit covered for 1 hour.
Fold in blueberries. After 1 hour, remove the cover. Add the blueberries to the bowl, and fold the dough over them until they’ve been well incorporated into the dough.
Long rise. Cover the dough with a towel, plate, or plastic wrap and let it rise for 8-12 hours or overnight.
Divide and rest. Remove the cover and transfer the dough to a clean, dry space. Divide the dough into 12 equal portions and form them into a ball. Cover and let them sit for 1 hour.
Prep the water bath. Add the water, honey, and baking soda (if using) to a large pot and bring to a boil over medium-high heat.
Prep for baking. While the water is coming to a boil, cut a piece of parchment paper into twelve 4x4-inch (2.5x2.5 cm) squares. Set aside. Line 2 baking sheets with parchment paper, then set aside. Preheat the oven to 375℉ (190℃).
Shape. Shape the dough balls into bagel shapes by pressing a hole into the middle and then stretching the hole. Place the prepared bagel onto one of the parchment squares. Repeat this process 11 more times until all the dough balls have been shaped into bagel shapes. The parchment paper allows for easy transfer, preventing the dough from sticking to your hands or the counter.
Boil. Working in batches (about 3 at a time), place the bagels into the water bath. Cook for 3 minutes, flipping halfway through (about 90 seconds). Transfer the boiled bagels to the lined baking sheet.
Bake. Bake the boiled bagels at 375℉ (190℃) for 25 minutes or until golden brown.
Cool. Remove them from the oven, cool for 5 minutes, then move them to a cooling rack. Cool on the rack for 10 minutes before cutting into them.