Preheat the oven to 400°F. Place a baking dish (usually 8x8 or 9x9) in the oven to warm while it heats.
Remove the hot dish, add the 1/2 cup unsalted butter, and let it melt completely in the warm pan. The butter should sizzle slightly and coat the bottom evenly.
In a large bowl, whisk together the 2 1/2 cups all-purpose flour, 1 tbsp granulated sugar, 4 tsp baking powder, 2 tsp kosher salt until well combined.
Pour in the 1 3/4 cups buttermilk and stir gently until a soft dough forms. Do not overmix. The dough should be thick but scoopable.
Pour the dough into the pan directly over the melted butter. Use a spatula to spread it evenly, letting the butter pool around the edges.
Use a knife to lightly mark lines in the dough to make cutting easier after baking.
Place the pan in the oven and bake for 20 to 25 minutes, or until the top is golden brown and the butter is bubbling around the edges.
Cool and serve. Let the biscuits rest for 5 minutes before slicing. Serve warm with jam, honey, or gravy.