In a mixing bowl, combine the sourdough starter and warm water. Stir to combine.

Add sugar, salt, and instant yeast to the mixture. Mix well.

Gradually add the flour to the wet ingredients, using a dough scraper or your hands to combine until a rough dough forms.

Knead the dough on a lightly floured surface for about 10 minutes, or until smooth and elastic.

Shape the kneaded dough into a ball and place it in a lightly greased bowl. Cover it with a damp cloth and let it rise for about 1 hour or until doubled in size.

Once the dough has risen, punch it down to release the air. Divide the dough into 8 equal pieces (about 90g each).

Shape each piece into a bagel by forming a ball and creating a hole in the center using your thumb. Gently stretch the hole to make it larger.

Preheat your oven to 425°F (220°C) and line a baking sheet with parchment paper.

In a large pot, bring water to a boil and add the baking soda.

Boil each bagel for about 30 seconds on each side. Remove with a slotted spoon and place them on the prepared baking sheet.

If desired, sprinkle your chosen toppings over the bagels while they are still wet.

Bake the bagels in the preheated oven for 20-25 minutes or until they are golden brown.

Once baked, remove the bagels from the oven and let them cool on a wire rack.