Arrange the oven shelf in the center of the oven. Preheat oven to 425ºF (218ºC). Place butter (1/2 cup) in a 10-inch cast iron skillet and place the dish in the oven, to melt, as the oven preheats. Remove the baking dish from the oven and set aside.
In a medium mixing bowl, using a pastry blender or 2 butter knives, cut the sour cream (1 cup) into Bisquick (4 cups).
Pour in the 7-up (1 cup) and mix just until combined. The dough should hold together but it will be very soft and sticky.
Lightly dust your clean counter with Bisquick. Turn the dough out onto the surface. Knead and fold dough until coated with your baking mix (just a few times). Gently pat the dough out to about 1 inch thick.
Use a biscuit cutter to cut the biscuits.
Place biscuits on top of butter in prepared skillet. Dot the tops of the biscuits with heavy cream (2-3 tablespoons). Bake in a preheated oven until the tops are golden, about 8-10 minutes.
Notes
Baking Pan: These can be baked in an 8-9 inch baking dish or a 9-inch cast iron skillet. Whichever pan you choose, you'll cut 9 biscuits. Can you use a larger cast iron skillet? Sure. The biscuits will just be thin.
Texture: This is a very wet dough. Handle gently and do not overmix.
Bench Bisquick: Use just enough Bisquick on your counter to prevent sticking.
Cutter: Use a biscuit cutter or cup. Dip the cutter into Bisquick to prevent sticking.