For the sand dollar, set a couche on a cutting board or sheet pan and sprinkle it liberally with rice flour. Scatter the handful of cornmeal onto a plate. Rock the preshaped loaves in the cornmeal to coat one half, and gently transfer them, cornmeal side up, onto the couche, which will let the dough relax more as it cold retards. Sprinkle the tops of the loaves with any remaining cornmeal. Arrange the couche around the sand dollar loaves to support their structure.