In a mixing bowl, combine the sourdough starter, warm water, sugar, and salt.

Gradually add the flour to the mixture, stirring until a shaggy dough forms.

Transfer the dough to a floured surface and knead for about 10 minutes.

Place the dough in a greased bowl, cover, and let it rise for 1 hour.

Once risen, punch down the dough, divide it into 8 pieces, and shape each into a bagel.

Place shaped bagels on a parchment-lined baking sheet and cover for another 30 minutes.

Bring a large pot of water to a boil, stir in the baking soda, and boil bagels for 1 minute on each side.

Transfer boiled bagels back to the baking sheet, add toppings, and bake at 425°F for 20-25 minutes.