Reprinted with permission by Harper Collins Publishing. From Mastering the Art of Japanese Home Cooking by Masaharu Morimoto. For a simple dashi udon broth, please see above.
Use rolling pin to roll out the dough, occasionally rotating the dough 90 degrees and lightly using with flour if it threatens to stick to the pin, until just between 1/8" to under 1/4" thick. If the dough is too difficult to roll out, cover with plastic wrap, let rest for 10 minutes, and then resume. This rest allows the gluten to relax and makes it easier to roll out.