-
1
Whisk flour, steel cut oats, flax seeds, yeast, and salt in large bowl. Add water and vinegar. Using rubber spatula, fold mixture, scraping up dry flour from bottom of bowl until shaggy, sticky ball forms. Cover bowl with plastic wrap. Let dough rest at least 12 hours, preferably about 18, at warm room temperature, about 70 degrees.
-
2
Lay 12X18-inch sheet of parchment paper inside 10-inch skillet and spray with nonstick cooking spray. Dough is ready when its surface is dotted with bubbles. Transfer dough to lightly floured work surface and knead 10 to 15 times. Shape dough into ball by pulling edges into middle. Transfer dough, seam-side down, to parchment-lined skillet and spray surface of dough with nonstick cooking spray. Cover loosely with plastic wrap and let rise at room temperature until dough has doubled in size and does not readily spring back when poked with finger, about 2 hours.
-
3
About 30 minutes before baking, adjust oven rack to lowest position, place 6-8 quart heavy-bottomed Dutch oven (with lid) on rack, and heat oven to 475 degrees. Lightly flour top of dough and, using razor blade or sharp knife, make one 6-inch-long, 1/2 inch-deep slit along top of dough.
-
4
Carefully remove pot from oven and remove lid. Pick up dough by lifting parchment overhang and lower into pot (let any excess parchment hang over pot edge). Cover pot and place in oven. Reduce oven temperature to 425 degrees and bake covered for 30 minutes. Remove lid and continue to bake until loaf is deep brown and instant-read thermometer inserted into center registers 210 degrees, 20 to 30 minutes longer. Carefully remove bread from pot; transfer to wire rack and cool to room temperature before slicing.
