Combine bread flour, all-purpose flour, and salt together in a large bowl. Mix in water slowly until dough comes together into a rough ball.
Turn dough out onto a work surface and knead until smooth and elastic, about 15 minutes. Wrap dough in plastic wrap and refrigerate, at least 3 hours or overnight.
Remove dough from the refrigerator and cut in half. Dust the dough, rolling pin, and your work surface with bread flour. Roll one piece of dough into a rectangle about 1/16-inch thick. Fold rectangle into thirds like a letter. Cut dough crosswise into thin strips. Repeat with second piece of dough.
Udon dough is traditionally kneaded with your feet. After mixing in step 1, place the ball of dough in a large resealable plastic bag and wrap in a thick towel. Step up and down on the towel with both feet until dough fills the bag and has an elastic texture, about 10 minutes.
Per Serving: 356 calories;1.3 g fat;
73 g carbohydrates;
11 g protein;
0 mg cholesterol;
585 mg sodium.