Preheat oven to 450˚F (230˚C). Grease a 10 inch (25 centimeter) round cast iron pan or baking dish with melted butter, then dust completely with flour.
In a large bowl, combine the 2 1/4 cups (280 grams) flour, baking powder, sugar, salt, and baking soda.
Cut in the diced cold butter using a dough blender, two forks, or your fingers until the mixture has a coarse texture with no pieces of butter larger than a pea.
Stir in the buttermilk just until combined with no streaks of flour remaining. Do not overwork.
Use a greased 1/4 cup (60 milliliters) measuring cup or ice cream scoop to drop rounds of dough onto the floured cast iron pan, arranging the rounds about 1/2 inch (1.25 centimeters) apart.
Dust the tops lightly with flour and brush with more melted butter.
Bake in the preheated oven for 5 minutes, then reduce the heat to 425˚F (220˚C). Continue to bake until the tops are golden in color, 12 to 15 minutes.
Allow the drop biscuits to cool in the pan for about 2 minutes before removing.
Serve warm on their own or with jam, butter, or honey.