Begin by preheating your oven to 375˚F. Grease a 10-inch cast-iron skillet generously with 1/2 Tbsp of butter to ensure the bread doesn’t stick.

In a spacious mixing bowl, combine the flour, sugar, salt, and baking soda, whisking them together until evenly distributed. Cut the cold butter into small pieces, then use your fingers to incorporate it into the dry ingredients until the mixture resembles coarse crumbs. If you're using raisins or dried cranberries, stir them in now, making sure to separate any clumps.

Create a well in the center of the mixture. In a large measuring cup, whisk together the buttermilk and egg until fully combined. Pour this into the well of the flour mixture. Using a wooden spoon, gently mix until the dough is just barely moistened and starts to come together—it’s crucial not to overwork the dough.

Turn the dough out onto a floured surface. With floured hands, shape it into a rough, round loaf. The dough should be shaggy and slightly sticky; if it’s too sticky to handle, lightly dust with more flour. Be careful not to overmix, as this will result in a tougher bread.

Place the formed dough into the prepared skillet. Use a sharp knife to score a deep “X” across the top of the loaf. Bake in the preheated oven for 50-55 minutes, positioning the skillet in the center of the oven. The bread is done when it sounds hollow when tapped on the bottom.

Transfer the loaf to a wire rack to cool completely. This bread is best enjoyed within two days of baking. Store any leftovers in the refrigerator, where they will keep for up to a week.