STEP 1

Stir together water and yeast, let stand 5 minutes. Stir in flours, oats, seeds, sugar, and salt. Knead briefly in bowl. Cover and let rest 30 minutes. Transfer to a lightly floured surface, and knead, with floured hands, until dough is smooth, but still a bit sticky, 3 to 5 minutes. Return to bowl, cover, and let rise until doubled in bulk, 1 1/2 to 2 hours.

STEP 2

Place a 5-quart enameled cast-iron Dutch oven on a rack set in the lower third of the oven (there should be no racks above it). Turn oven to 475° and heat, with pot inside, for 1 hour.

STEP 3

Meanwhile, on a lightly floured surface, with floured hands, fold edges of dough into center to create a tight bundle: Start by folding edge closest to you in toward center. Then fold in sides, as if creating an envelope; finally, fold top edge down. Flip dough seam-side down. Using both hands, and keeping the sides of your hands in contact with work surface, cup side of dough farthest from you and gently drag it down toward your body in a half-circle motion, simultaneously using the side of your hand to tuck edges under dough round. (This will create tension on the outside of the dough, which is necessary to maintain the shape of the finished loaf.) Continue rotating and dragging until dough is taut, and uniformly round, 3 to 4 more turns.

STEP 4

Line a smaller bowl (about 10 inches across) with parchment paper, leaving a generous overhang. Place dough in bowl and lightly drape with plastic wrap. Let rise in a warm spot until slightly more than doubled in bulk (it should rise above top of bowl), 1 to 1 1/2 hours.

STEP 5

Brush top of dough with egg white and sprinkle with sesame and poppy seeds. Using a razor blade or a very sharp knife, score surface in a decorative pattern. Lift dough using parchment overhangs and transfer to the hot pot. Be careful as all the parts of the pot will be very hot!

STEP 6

Sprinkle lightly with water. Cover, and place in oven. Reduce heat to 450° and bake 40 minutes. Remove lid; bake until deep golden brown and a thermometer inserted in center reads 205°, 5 to 15 minutes more. Let cool in pot on a wire rack 15 minutes, then turn bread out onto rack to cool completely.