Step 1

Stir together 3 cups whole-wheat flour, bread flour, oats, salt, yeast, 1/4 cup pumpkin seeds, and 2 tablespoons each flax, poppy, and sesame seeds in a large bowl. Whisk honey or sugar into water in measuring cup, then stir into flour mixture. Drizzle a thin layer of oil over top of dough, cover with plastic wrap, and refrigerate 2 hours, then let rise at room temperature 12 to 18 hours.

Step 2

Coat inside of a large Dutch oven or ovenproof pot with oil and sprinkle evenly with 2 tablespoons whole-wheat flour. Stir dough to deflate, then quickly form into a ball and place in pot. Sprinkle with remaining 1 tablespoon whole-wheat flour and smooth into dough with your hands. Brush with egg white and sprinkle with remaining 1 tablespoon each pumpkin, flax, poppy, and sesame seeds. Cut an X in top of dough with a sharp knife. Cover; let rise in a warm spot until doubled in bulk, about 1 1/2 hours.

Step 3

Preheat oven to 475 degrees with a rack in lower third. Lightly sprinkle top of dough with water, cover, and place in oven. Reduce oven heat to 450 degrees. Bake until browned, about 45 minutes. Remove lid; bake 15 minutes more. Let cool in pot on a wire rack 15 minutes, then turn bread out onto rack to cool completely. To store, wrap tightly in plastic and keep at room temperature up to three days.