Make a sponge by combining 1–1/2 cups warm water, 2 heaping TBL dry yeast and 2 cups bread flour. Cover and let rise until doubled. Meanwhile, dissolve 1/3 cup corn starch into 1/3 cup cold water; use your fingers to be sure there are no lumps remaining. Combine with 1 cup boiling water in a small saucepan and return to heat. Cook briefly until it turns into a semi-transparent gelatinous mass.
When the sponge is ready, combine the sponge, the cooled cornstarch mixture, 1–1/2 cups corn flour, 3 cups bread flour and 1–1/2 TBL salt. Mix on low speed for 5-8 minutes or knead by hand. You will need to add more flour, but the dough should still be wet.
Form into 2 long or 3 round loaves. Dust with potato starch or flour and let rise on baking sheets dusted with cornmeal. Rise, covered, for 45 minutes, then bake at 475 F convection for 45 minutes.
Adapted from Secrets of a Jewish Baker.