1) Whisk together the cornmeal and salt.
2) Add the butter and molasses to the bowl.
3) Pour in the boiling water, stirring until the butter has melted and the mixture is smooth. Let the mixture cool to lukewarm, about 15 minutes.
4) Mix in the dry milk, flours, and yeast. Let the dough rest for 20 minutes; this gives the flours and cornmeal a chance to absorb the liquid.
5) Knead the dough for about 7 minutes at medium speed of a stand mixer, until it's smooth. It'll be quite stiff, but still fairly sticky on the surface. Cover the bowl, and let the dough rise until it's just about doubled, about 1 hour.
6) Gently deflate the dough, and shape it into an 8" log. Place the log in an 8 1/2" x 4 1/2" loaf pan, cover the pan, and let the dough rise until the center has crested at least 1" above the lip of the pan, about 90 minutes.
7) Towards the end of the rising time, preheat the oven to 350°F.
8) Bake the bread for 35 to 40 minutes, until an instant-read thermometer inserted into the center registers at least 190°F. You may want to tent the bread loosely with aluminum foil for the final 15 minutes of baking, if you prefer a lighter crust.
Yield: 1 sandwich loaf.