Set up the couche: Lay out your couche and dust it with a 50/50 mixture of bread flour and rice flour.
Preheat oven: Preheat your oven to 500°F with your baking stone and lava rocks or cast iron skillet inside.
Flour and flip: Flour the surface of the dough in the container with bread flour. Use a plastic scraper to gently detach the edges, then flip the dough onto your work surface.
Degas and divide: Keep the dough in a rectangular shape and gently degas it evenly with the palm of your hand. Divide into 3 even pieces with clean, confident cuts.
Preshape: For each piece, fold the top edge down about ⅔ of the way and the bottom edge up about ⅔ of the way, like a letter fold. Fold down the middle and use the ball of your hand to seal the seam into a rough batard shape.
Bench rest: Cover and rest for 20 minutes.