Feed your sourdough starter 4-12 hours before mixing. Mix equal weights of starter, flour, and water and let sit at room temperature until bubbly and doubled. Test readiness by dropping a small spoonful in water—if it floats, it's ready.
In your mixing bowl, combine 100g active starter, 240ml warm water, and 15g barley malt syrup or honey until dissolved. Add 500g bread flour and 10g salt, then knead with a dough hook for 6-8 minutes or by hand for 10-12 minutes until smooth, stiff, and slightly tacky.
Shape the dough into a ball, place in the bowl, and cover with plastic wrap. Let ferment at room temperature for 4-8 hours until puffed and risen by 50-75%. The dough should feel alive but may not double completely.
Turn the dough onto a floured surface and divide into 8 equal pieces (about 105-110g each). Shape each piece into a ring by rolling it into a log, wrapping around your hand, and sealing the ends firmly together on the counter.
Place shaped bagels on a parchment-lined baking sheet and cover loosely with plastic wrap. For same-day baking, proof for 2-3 hours at room temperature. For best flavor, cold proof in the fridge for 8-16 hours.
Preheat your oven to 450°F (232°C) at least 30 minutes before baking. Bring a large pot of water to a rolling boil and add 2 tablespoons of honey or barley malt syrup.
Boil 2-3 bagels at a time for 1 minute per side. For a chewier crust, boil for 90 seconds per side. Remove with a slotted spoon and place back on the baking sheet.
Whisk the egg with 1 tablespoon of water and brush over the boiled bagels. Immediately sprinkle your desired toppings (everything seasoning, sesame seeds, poppy seeds, or coarse salt) and press gently to adhere.
Bake at 450°F (232°C) for 20-25 minutes until deep golden brown. Rotate the pan halfway through for even baking. Transfer to a wire rack and cool for at least 15 minutes before slicing.