Preheat the oven to 450 degrees F. Place a 10 1/2-inch cast-iron skillet in the oven to heat.
Add the flour to a large bowl. Use your hands or a pastry cutter to work the shortening into the flour until the crumbs are the size of large peas.
Slowly pour in the buttermilk, then mix with your hands until the mixture starts to form a dough. Add buttermilk if it feels too dry. As soon as the dough comes together, transfer to a floured work surface. Press the dough into a square and fold it over itself to create layers, using additional flour to keep the dough from sticking. Shape into a 1/2-inch-thick rectangle. Use a 2- to 3-inch biscuit cutter to cut out biscuits, rerolling the scraps to use all the dough.
Take the skillet out of the oven and add 2 tablespoons melted butter. Place the biscuits in the skillet, then lightly brush the tops with the remaining butter.
Bake until lightly golden brown, 15 to 17 minutes. Let cool for a few minutes, then serve.