Preheat your oven to 450°F (230°C) and place a cast-iron skillet or baking sheet in the oven to heat up.
In a large mixing bowl, whisk together the flour, sugar, salt, baking powder, and baking soda.
Make a well in the center of the dry ingredients and pour in the buttermilk and melted butter. Stir until just combined.
Lightly flour your hands and work surface. Turn the dough onto the floured surface and shape it into a round loaf.
Transfer the shaped dough to a piece of parchment paper and score the top of the loaf with an 'X' or crosshatch pattern.
Carefully transfer the dough (with the parchment paper) to the preheated skillet or baking sheet and bake for 15–20 minutes.
Brush the top with melted butter as soon as the bread comes out of the oven and let it cool slightly before slicing.
