1 cup flour
1 teaspoon baking powder
1/4 teaspoon baking soda
1/2 teaspoon sugar
1/2 teaspoon salt
1/2 cup buttermilk (cold)
1/4 cup butter, melted and cooled slightly (about 5 minutes)
Adjust oven rack to middle position and heat oven to 475 degrees.
Whisk flour, baking powder, baking soda, sugar, and salt in large bowl. Combine buttermilk and 1/4 cup melted butter in medium bowl, stirring until butter forms small clumps
Add buttermilk mixture to dry ingredients and stir with rubber spatula until just incorporated and batter pulls away from sides of bowl.
Using greased 1/4-cup dry measure, scoop a scant amount of batter and drop onto parchment-lined rimmed baking sheet. Repeat with remaining batter, spacing biscuits about 1 1/2 inches apart.
Bake until tops are golden brown and crisp, 10 to 13 minutes. They can be made up ahead of time and gently re-heated in a 300 oven for 10 minutes.
Brush biscuit tops with 1 tablespoon melted butter. Transfer to wire rack and let cool 5 minutes before serving.