Before scooping your flour, fluff it up with a whisk or large spoon. Use the scoop and level method for measuring.
Measure the 3 cups flour into a large mixing bowl, or the bowl of a stand mixer. Add the sugar, salt, baking soda, and instant yeast. Whisk together briefly.
Combine the milk, water, and oil in a separate, microwave-safe bowl, and heat to between 120°F and 130°F. Be sure to stir the liquid well before measuring its temperature; you want an accurate reading. If you don't have a thermometer, the liquid will feel quite hot (hotter than lukewarm), but not so hot that it would be uncomfortable as bath water.
Pour the hot liquid over the dry ingredients in the mixing bowl.
Using an electric beater, or stand mixer with paddle attachment, beat at low speed for 10 seconds, then beat at high speed for 1 minute; the dough will be smooth and very soft. If you don't have an electric mixer, beat by hand for 2 to 3 minutes, or until the dough is smooth and starting to become elastic.
Lightly grease an 8 1/2" x 4 1/2" loaf pan, and sprinkle the bottom and sides with cornmeal.
Scoop the dough into the pan, it's a little rubbery now, leveling it in the pan as much as possible. Using your fingers, coated with a tiny bit of oil, helps to achieve this.
Spray plastic wrap with cooking spray or lightly coat with some oil (so the dough doesn't stick to it when it rises). Cover the pan with the plastic, and let the dough rise till it's just barely crowned over the rim of the pan. When you look at the rim of the pan from eye level, you should see the dough, but it shouldn't be more than, say, 1/4" over the rim. This will take about 45 minutes to 1 hour, if you heated the liquid to the correct temperature and your kitchen isn't very cold. While the dough is rising, preheat the oven to 400°F.
Remove the cover, and bake the bread for 22 to 27 minutes, till it's golden brown and its interior temperature is 190°F. During the last 15 minutes or so of baking, feel free to lightly tent some aluminum foil over the bread if you think it's browning too quickly. I do this every time after 9 or 10 minutes of baking and after 22 minutes of baking are complete I check the internal temperature and if it needs additional baking time, I keep the foil on.
Remove the bread from the oven and immediately melt about 1/2 tablespoon of butter or oil over the top and then sprinkle top with a light dusting of corn meal (this step is optional but makes the top look nice). After 5 minutes turn it out of the pan onto a rack to cool. Let the bread cool completely before slicing.