Preheat the oven to 375˚F and generously grease a 10” cast-iron skillet with 1/2 tablespoon butter.
In a large mixing bowl, whisk together the flour, sugar, salt, and baking soda.
Cut the butter into small pieces and work it into the flour with your fingers until the mixture resembles coarse crumbs.
Stir in the raisins, making sure to break up any clumps.
In a separate measuring cup, whisk the buttermilk and egg together, then pour it into the flour mixture.
Stir gently with a wooden spoon until just combined and the dough barely starts to come together.
Transfer it onto a floured surface and, using floured hands, shape it into a round loaf, keeping the texture shaggy.
If the dough is too sticky, dust lightly with flour, but avoid over-mixing to prevent toughness.
Place the dough into the buttered skillet, then use a sharp knife to cut a deep “X” on top.
Bake in the center of the preheated oven for 50-55 minutes, until the bread sounds hollow when tapped.
Transfer to a wire rack to cool before slicing.