Combine warm water, yeast, and sugar in a bowl. Set aside until dissolved, about 5 minutes.
Combine bread flour, whole wheat flour, rolled oats, vital wheat gluten, wheat germ, flaxseed meal, and sea salt in a large bowl. Stir in buttermilk. Add the yeast mixture and honey; stir until no dry spots remain. Cover bowl with plastic wrap and let dough rest 20 minutes.
Turn dough onto a floured work surface. Knead about 7 minutes; it will be soft and slightly sticky. Add more flour if needed. Shape into a ball. Spray a mixing bowl with cooking spray. Place dough in the bowl and turn to coat. Cover with plastic wrap and let rise for 2 hours in warm, draft-free place.
Preheat oven to 400 degrees F (200 degrees C). Line one 11x17-inch baking sheet with waxed paper, another with a flour sack towel, and 2 remaining sheets with parchment paper sprinkled with cornmeal.
Combine 3 quarts water and brown sugar in a large pot; bring to a boil.
Turn dough onto a floured surface; knead briefly. Cut dough in half; return 1 half to the bowl and cover. Form the other half into a cylinder. Cut into quarters and cut quarters in half, yielding 8 equal-sized pieces of dough. Shape dough pieces into balls. Repeat with remaining half of dough.
Flatten a dough ball slightly; press index fingers through the center until they meet. Rotate fingers to stretch a hole about 1 3/4-inch in diameter. Set bagel on waxed paper-lined baking sheet. Repeat with remaining dough balls.
Reduce heat to simmer under the sugar-water mixture. Boil 2 bagels at at time; cooking each for 30 seconds per side. Transfer boiled bagels to the towel-lined baking sheet to drain. Transfer bagels to the parchment paper-lined sheets.
Mix egg white and 1 teaspoon cool water together in a small bowl; use mixture to brush tops of bagels.
Bake in the preheated oven for 12 minutes. Flip bagels and continue baking until golden brown, about 13 minutes more.
