Preheat oven to 375°F. Brush the bottom and sides of a large 10 or 12 inch cast iron skillet with oil.
In a large bowl, use a whisk to sift together flour, sugar, baking soda, baking powder and salt. Add butter, cutting into the flour using a pastry blender.
Whisk together 1 1/2 cup buttermilk and egg. Add to the dry ingredients and raisins mixing until fully moistened.
Turn dough out onto a non stick lightly floured surface and knead lightly just until it comes together using floured hands. Form into roughly an 8 inch round and place into skillet. (You can also bake on a parchment lined baking pan.)
In a small bowl, combine melted butter with reserved 1/4 cup buttermilk. Brush loaf on all sides. Use a sharp knife to cut an 'X' into the center to vent.
Bake for 40-50 minutes or until crusty on the outside and baked through. Check center of loaf with a toothpick to test for doneness. Continue to baste periodically with buttermilk and melted butter. (If butter cools and solidifies, heat in the microwave for a few seconds to melt)
Cool in the skillet for 10 minutes then move to a cooling rack to cool completely.
Store in an airtight container at room temperature for up to 2 days.