Preheat oven to 350°. Add parchment paper to the cast iron skillet, about 10-12 inches.
Whisk the flour, soda, powder, salt, sugar, and raisins in a large mixing bowl. At this time, melt the butter in a small saucepan over medium heat.
Add the buttermilk, melted butter, and egg to the dry ingredients, and mix until all is incorporated. Don't over mix. It should appear super wet.
Pour the batter into the cast iron with the lined parchment. (or in two smaller ones) Use a spatula to smooth the top. Sprinkle about a tablespoon of sugar on top. Bake for 1 hour. To check to doneness, use a wooden stick by inserting in the middle of the cake. It should come out clean.