Preheat the oven. Preheat the oven to 425°F.
Combine the sour cream and soda. Add the sour cream to a mixing bowl. Slowly pour in the 7UP or Sprite while whisking. The soda will fizz, so add it gradually until the mixture is evenly combined.
Make the biscuit dough. Add the Bisquick to a large mixing bowl, then pour in the sour cream mixture. Stir until just combined. The dough will be very sticky.
Prepare the dough. Generously dust your work surface and hands with all-purpose flour. Transfer the dough onto the floured surface, sprinkle additional flour over the top, and gently pat it to approximately 1 inch thick.
Cut the biscuits. Lightly wet a biscuit cutter, then dip it into flour to prevent sticking. Press straight down into the dough to cut the biscuits. Gently gather and press out the remaining dough, adding flour as needed, until you've cut as many biscuits as possible. The dough should yield approximately 12–13 biscuits.
Prepare the baking dish. Melt ½ cup of salted butter and pour it into a 9×9-inch baking dish. Arrange nine biscuits in the melted butter. Reserve the remaining cut biscuits for a separate batch.
Bake. Bake at 425°F for approximately 20–25 minutes, until the biscuits have risen and the tops are golden brown.
Finish with butter. Remove the biscuits from the oven and brush their tops with 1–2 tablespoons of additional melted salted butter before serving.