Set your oven to 450°F (232°C) and allow it to preheat fully.

In a spacious mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt until uniformly blended. Pour in the buttermilk and stir gently until a loose, somewhat lumpy dough develops. Avoid overmixing. Let the mixture sit for 5 minutes to hydrate.

Place the butter in an 8 or 9-inch square baking dish. Insert the dish into the oven for 3 to 5 minutes, or until the butter has fully liquefied. Carefully remove the hot pan.

Using a spatula, spoon the dough into the pan over the melted butter. Spread it out lightly until it evenly reaches all four edges. Some melted butter may rise to the surface — this is expected and contributes to the final texture.

Lightly coat a bench scraper or large kitchen knife with cooking spray. Cut the unbaked dough into a 3x3 grid, yielding nine squares. Wipe and respray the blade as needed, making a second pass along the lines to define the sections. The dough will be fluid, and the cuts may begin to close — this is normal.

Slide the pan into the oven and bake for 20 to 25 minutes, rotating the dish halfway through to ensure even browning. The biscuits are ready when the tops are golden and they have begun to pull away from the pan's edges. Butter may still be bubbling along the sides.

Remove the biscuits from the oven and allow them to rest for at least 5 minutes. This brief pause lets the butter finish soaking into the layers. Cut along the pre-scored lines and serve warm.