Lightly grease an 8½x4½-inch loaf pan with cooking spray. Dust the bottom and sides with cornmeal. Set aside.
In the bowl of a standing mixer fitted with the paddle attachment or a large mixing bowl, whisk together the whole wheat flour, all purpose flour, vital wheat gluten flour (if using), brown sugar, yeast, salt, and baking soda.
In a microwave-safe bowl or large glass measuring cup, combine the milk, water, and oil. Microwave in 30 second intervals, until the liquid reaches 120-130°F. Stir the liquid together well before taking the temperature, and for best results, use a digital read thermometer.
Pour the warm liquids over the dry ingredients, then beat the mixture on high speed for one minute. The dough will be very soft, somewhat sticky, and moist. Transfer the dough to the prepared pan, then press it gently with the back of your hand to make it as even as possible.
Lightly grease a sheet of plastic wrap with cooking spray, then cover the pan and let rise in a warm, draft-free place, until the dough just barely rises over the top rim of the pan, about 1 hour, depending upon the temperature of your kitchen. (Alternatively, you can place the loaf in your refrigerator to rise overnight. Let stand at room temperature for 30 minutes prior to baking.) Towards the end of the rise time, place a rack in the center of the oven and preheat oven to 400°F.
Once dough has risen, remove the plastic wrap and bake for 22 to 27 minutes, until it is golden brown and the interior temperature registers 185-190°F. Check the dough at the 15-minute mark—if it is browning too quickly, lightly tent the pan with foil, then continue baking until the bread is done. Remove the bread from the oven and let stand for 5 minutes in the baking pan. Gently turn the bread out from the pan and place on a cooling rack. Allow bread to cool completely before slicing.