Preheat your oven to 350°F (175°C). Grease a standard 9x5-inch loaf pan.
In a large bowl, whisk together the flour, sugar, baking soda, baking powder, and salt.
In a separate bowl, whisk the melted butter, oil, eggs, and buttermilk together until smooth.
Pour the wet ingredients into the dry ingredients. Stir with a spoon or spatula just until flour disappears (do not overmix, or the bread will get tough).
Scrape the batter into your greased loaf pan. Bake for 45 to 55 minutes or until a toothpick inserted into the center comes out clean.
Let it cool in the pan for 10 minutes, then move it to a wire rack to cool completely before slicing.