Preheat the oven to 350 degrees F., and spray three mini loaf pans (or 1 regular loaf pan) with nonstick spray.
Melt the butter in a glass dish in the microwave, and then set it aside to cool.
In a large bowl, use an electric mixer to combine the milk, buttermilk and eggs. Mix on medium speed for 2 minutes.
In a separate medium bowl, whisk together the cornmeal, flour, sugar, baking powder, baking soda and salt.
Add half of the dry ingredients to the wet ingredients in the bowl and mix for about 30 seconds. Add the remaining dry ingredients and mix just until incorporated, scraping down the sides of the bowl as needed. Mix in the melted butter.
Pour the batter into the prepared pans (or just one pan if you're using a regular-sized loaf pan). Bake for 10 minutes, rotate the pans, and then bake for an additional 10 minutes, or until a toothpick inserted into the center comes out clean. If you are baking this cornbread in a larger loaf pan, it should take about 40 minutes to bake.