01 - Combine active sourdough starter, lukewarm water, and sugar in a large mixing bowl. Stir thoroughly until sugar completely dissolves.
02 - Add bread flour, whole wheat flour, and sea salt to the starter mixture. Mix with a wooden spoon until shaggy dough forms.
03 - Turn dough onto lightly floured surface. Knead for 8 to 10 minutes until smooth and elastic. Drizzle with vegetable oil during final 2 minutes of kneading.
04 - Gently fold raspberries into dough, handling lightly to keep berries whole. Dough will appear sticky with pink marble streaks.
05 - Place dough in greased bowl, cover with plastic wrap, and let rise at room temperature for 6 to 8 hours until doubled in size.
06 - Turn risen dough onto floured surface. Divide into 8 equal portions using a dough scraper or bench knife.
07 - Roll each portion into smooth ball. Press thumb through center to create hole, then gently stretch opening to 2 inches wide. Place on parchment-lined baking sheet.
08 - Cover shaped bagels with clean kitchen towel. Let proof at room temperature for 1 to 2 hours, or refrigerate overnight for deeper flavor development.
09 - Preheat oven to 425°F with oven rack positioned in center.
10 - Bring 12 cups water to rolling boil in wide pot. Stir in honey or malt syrup until dissolved. Add baking soda if using for extra chewiness.
11 - Working in batches, gently drop bagels into boiling water. Boil for 45 to 60 seconds per side. Remove with slotted spoon, draining well, and return to baking sheet.
12 - Sprinkle wet bagels immediately with Demerara sugar or poppy seeds while surface is still tacky.
13 - Bake for 22 to 25 minutes until deeply golden brown. Transfer to wire rack and cool completely before slicing.