01 - Heat olive oil in a skillet over medium-low heat. Add sliced onions and 1/2 teaspoon salt. Cook, stirring occasionally, until deeply caramelized and golden brown, approximately 20 to 25 minutes. Remove from heat and set aside to cool completely.
02 - In a large mixing bowl, combine the active sourdough starter, warm water, and honey. Whisk thoroughly until the honey dissolves completely into the mixture.
03 - Add bread flour, whole wheat flour, and sea salt to the wet ingredients. Mix until a rough dough forms. Turn onto a lightly floured surface and knead for 8 to 10 minutes until the dough becomes smooth, elastic, and passes the windowpane test.
04 - Place the kneaded dough in a lightly oiled bowl, turning once to coat all surfaces. Cover with a damp cloth or plastic wrap. Let rest at room temperature for 4 to 6 hours, or until the dough has doubled in size.
05 - Turn the dough onto a floured surface and divide into 8 equal portions. Shape each piece into a tight ball by tucking the edges underneath. Poke a hole through the center with your finger and gently stretch to form a 2-inch opening, creating the classic bagel shape.
06 - Arrange shaped bagels on a parchment-lined baking sheet, leaving space between each. Cover loosely with plastic wrap. Let proof at room temperature for 1 hour, then refrigerate overnight for 8 to 12 hours to develop flavor.
07 - Preheat oven to 425°F.
08 - Bring 2 quarts of water and barley malt syrup (or honey) to a gentle boil in a large saucepan or Dutch oven. Reduce heat to maintain a steady simmer.
09 - Remove bagels from the refrigerator. Working in batches if necessary, boil each bagel for 45 seconds per side, using a slotted spoon to gently flip. Transfer boiled bagels back to the parchment-lined baking sheet.
10 - Immediately press the cooled caramelized onions onto the tops of the boiled bagels, ensuring they adhere securely to the surface.
11 - Bake for 20 to 25 minutes, rotating the baking sheet halfway through, until bagels are deeply golden brown with a crisp, shiny crust.
12 - Transfer bagels to a wire rack and let cool for at least 30 minutes before slicing. This completes the cooking process and ensures proper texture.