1. Preheat the oven to 325 degrees F (165 degrees C). Grease a 9x5-inch loaf pan.
2. Combine flour(3 cups), baking powder(1 tbsp), sugar(1/3 cups), salt(1 tsp), and baking soda(1 tsp) in a large bowl. Lightly beat egg(1) and buttermilk(2 cups) together; add all at once to the flour mixture and mix just until moistened. Stir in melted butter(1/4 cups). Pour into prepared pan.
3. Bake in the preheated oven until the top is golden brown, about 65 to 70 minutes. A toothpick inserted into the bread should come out clean. Cool on a wire rack. Wrap in foil for several hours, or overnight, for best flavor.