In a large mixing bowl, combine the sourdough starter and warm water. Stir until well mixed.

Add the bread flour, sugar, and salt to form a dough.

Turn the dough out onto a floured surface and knead for about 10 minutes.

Place the dough in a lightly greased bowl and cover it with a damp cloth. Let it rise for about 1-2 hours, or until it doubles in size.

Once risen, punch down the dough and divide it into 8 equal pieces.

Shape each piece into a ball, then poke a hole in the center with your finger and gently stretch it to form a bagel shape.

Place the shaped bagels on a baking sheet lined with parchment paper. Cover them with a damp cloth and let them rise for another 30-45 minutes.

Preheat your oven to 425°F (220°C).

Bring a large pot of water to a boil and add the baking soda.

Gently lower the bagels into the boiling water, cooking for 1-2 minutes on each side.

Transfer the boiled bagels back to the baking sheet and sprinkle with your desired toppings.

Bake for 20-25 minutes until golden brown.