01 - Combine active sourdough starter, lukewarm water, and sugar in a large mixing bowl. Stir continuously until sugar completely dissolves and mixture is uniform.
02 - Add bread flour, whole wheat flour, and sea salt to the starter mixture. Mix with a wooden spoon until shaggy dough forms and no dry flour remains visible.
03 - Turn dough onto lightly floured surface. Knead for 8 to 10 minutes until smooth and elastic. Drizzle vegetable oil onto dough during final minute of kneading and work until fully incorporated.
04 - Gently fold fresh raspberries into dough, taking care to keep berries whole. Dough will appear sticky and show raspberry marbling throughout.
05 - Transfer dough to a lightly greased bowl. Cover with plastic wrap or damp towel. Let rise at room temperature for 6 to 8 hours until doubled in volume.
06 - Turn risen dough onto lightly floured surface. Using a dough scraper or knife, divide dough into 8 equal pieces, approximately 4 ounces each.
07 - Roll each portion into a smooth ball. Press thumb through center of each ball to create a hole. Gently stretch and rotate dough to form bagel shape with 2-inch diameter opening.
08 - Arrange shaped bagels on parchment-lined baking sheet. Cover with clean kitchen towel. Let proof at room temperature for 1 to 2 hours. For enhanced flavor development, refrigerate overnight.
09 - Set oven to 425°F. Ensure oven rack is positioned in center of oven.
10 - Bring 3 quarts water to rolling boil in wide pot. Stir in honey or barley malt syrup. Add baking soda now if using for extra chewiness.
11 - Working in batches of 2 to 3, carefully lower bagels into boiling water. Boil for 45 to 60 seconds per side. Remove using slotted spoon, allowing excess water to drain, then return to parchment-lined baking sheet.
12 - Immediately sprinkle tops of wet bagels with Demerara sugar or poppy seeds if desired. Topping adheres best while bagels are still damp from boiling.
13 - Place baking sheet in preheated oven. Bake for 22 to 25 minutes until bagels develop deep golden brown color and shiny crust. Rotate baking sheet halfway through baking for even browning.
14 - Transfer baked bagels to wire rack. Cool completely for at least 30 minutes before slicing or serving. This completes texture development.