Preheat an oven to 350 degrees Fahrenheit and spray a 9-inch loaf pan with non-stick cooking spray.
In a large bowl, whisk together the 2 cups whole wheat flour, 1 cup all-purpose flour, ½ cup rolled oats,1 ½ teaspoons salt, and 2 teaspoons baking soda.
In a separate bowl, mix the 2 cups room temperature buttermilk, ¼ cup molasses, and 3 tablespoons melted unsalted butter. Pour the buttermilk mixture into the flour mixture and mix until the dough just comes together.
Place the dough into the loaf pan and even out the top, sprinkle with some oats, and bake for 50-55 minutes, a toothpick inserted should come out clean, or temp out to 190 degrees Fahrenheit.
Remove from the oven and let the loaf cool in the pan for 5 minutes, then remove and let it cool completely on a cooling rack.