Prepare the Dough:

1. In a large bowl, mix together the sourdough starter, bread flour, water, salt, and barley malt syrup until a sticky dough forms.
2. Knead the dough by hand for 10-15 minutes or use a stand mixer with a dough hook on medium speed for 8-10 minutes until smooth and elastic.

First Rise (Bulk Fermentation):

1. Cover the bowl with a damp cloth or plastic wrap.
2. Let the dough rise at room temperature (75-80°F or 24-27°C) for 4-6 hours, or until it doubles in size.

Shape the Bagels:

1. Divide the dough into 8 equal portions (approximately 100-110 grams each).
2. Roll each portion into a ball, then poke a hole in the center and gently stretch it to form a ring.
3. Place the shaped bagels on a parchment-lined baking sheet.

Second Rise (Proofing):

1. Cover the bagels with a damp cloth.
2. Let them proof at room temperature for 1-2 hours, or until puffy.
3. For a more pronounced sour flavor, refrigerate the bagels overnight and bake the next day.

Boil the Bagels:

1. Preheat the oven to 425°F (220°C).
2. Bring a large pot of water to a boil and add 1 tablespoon of baking soda.
3. Carefully drop the bagels into the boiling water, a few at a time, and boil for 1-2 minutes on each side.
4. Remove with a slotted spoon and return to the baking sheet.

Bake the Bagels:

1. Bake in the preheated oven for 20-25 minutes, or until golden brown.
2. For an extra-crispy crust, turn off the oven and leave the bagels inside for an additional 5 minutes with the door slightly ajar.