In a large bowl, add the flour, baking powder, baking soda, and salt. Whisk this dry mixture together gently to blend, about a minute.
Using a pastry blender, cut in the butter until it resembles coarse crumbs.
Slowly pour in the buttermilk. I like to use a butter knife to “cut” through the mixture until a dough forms. I find that this helps keep the dough tender. Keep dragging the knife through the dough to incorporate the buttermilk. If you find some dry areas at the bottom of the bowl, add a splash or two until all of the dough is moistened.
Now, grab a small ball of dough and roll in your hand like a meatball. Then roll the ball and coat all sides in flour.
Make sure the inside of your cast iron skillet is lightly coated in some oil (vegetable oil), this will keep them from sticking.
Place the dough balls in the skillet, evenly spaced.
Bake for 20-25 minutes until the tops are golden brown.
If you want extra buttery biscuits, melt ½ cup of butter and brush the tops of the biscuits once they come out of the oven.