Preheat oven to 450°F
Place sliced butter in an 8×8-inch baking dish and bake 5–7 minutes until melted and bubbling, then remove from oven
In a large bowl, whisk flour, baking powder, salt, and sugar
Add buttermilk and melted butter, then stir just until combined (batter will be thick)
Pour batter directly over melted butter without stirring
Gently spread to edges and cut into 9 squares
Bake 22–30 minutes until golden and cooked through (place lined pan underneath to catch spillage and tent loosely with foil around 22 minutes if needed)
Optional: Brush tops with melted butter and sprinkle lightly with Maldon salt after removing from oven
Rest 5 minutes before cutting
