Preheat your oven. Preheat your oven to 425°F (220°C), then place your 8-inch cast iron skillet inside it while it preheats to make sure the skillet is hot when the biscuits are added.
Prepare the dry ingredients. In a mixing bowl, whisk together the self-rising flour and sugar. Then, add the diced butter. Using a pastry blender, two knives, or your hands, cut in the butter until the mixture resembles coarse crumbs with some larger pea-sized pieces.
Add the buttermilk. Pour the buttermilk into the flour mixture. Gently stir with a spatula until the dough just comes together. It will be slightly sticky but should hold its shape. Avoid overmixing.
Form the dough. Lightly flour a clean counter or large cutting board. Turn the dough out onto the surface and knead it a few times, just until it smooths out. Be careful not to overwork the dough.
Roll and cut the biscuits. Roll the dough out to ¾-inch thickness using a rolling pin. Use a 2¼-inch round biscuit cutter to cut out biscuits, pressing straight down without twisting to make sure they rise evenly. Gather any scraps, gently reform them, and cut additional biscuits.
Prepare the skillet. Carefully remove the hot cast iron skillet from the oven. Then, melt 2 tablespoons of butter in the skillet over medium heat on the stovetop. Once melted, pour most of it into a small bowl, leaving a thin layer in the skillet to coat the bottom.
Bake. Place the skillet back in the oven and bake the biscuits for 16 minutes until golden brown and cooked through.
Serve. Allow the biscuits to rest for a couple of minutes before serving. Enjoy them warm with butter, honey, or your favorite jam.