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

Gradually add in the flour and salt. Mix until a rough dough forms.

Transfer the dough to a floured surface and knead for about 10 minutes until it becomes smooth and elastic.

Place the dough in a lightly greased bowl and cover it with a cloth. Allow it to rest for about an hour until it has doubled in size.

After resting, punch down the dough and divide it into 8 equal pieces.

Roll each piece into a ball, then poke a hole in the center to form a bagel shape. Make sure the hole is wide enough, as it may shrink during cooking.

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

Carefully drop the bagels in and boil for about 30 seconds on each side.

Remove and place on a baking sheet lined with parchment paper.

Whisk the egg in a small bowl and brush the top of each bagel with the egg wash.

Add your desired toppings.

Preheat your oven to 425°F (220°C).

Bake for 20-25 minutes, or until they are golden brown.

Once done, let them cool on a wire rack.