Preheat oven to 400F and grease a 9” or 10” cast iron skillet (or similar pan) with softened butter.
In a large bowl, whisk together flour, baking soda, sugar, and salt.
Grate in frozen butter and then use fingers to work it into the flour mixture to form little crumbs.
Add in buttermilk and stir to combine. Add in raisins and mix again. Will likely need to use hands to work together until it is all just combined and form into an 8” round disc. Make sure not to over mix.
Place in skillet and make a X on the top about 1” deep. Brush with extra buttermilk.
Bake for about 45-50 minutes. Bake until golden brown. Bottom should sound hollow when tapped. Remove from oven and cool for at least 15 minutes before cutting.
Store in an airtight container for up to 2-3 days at room temperature.