Adjust oven rack to middle position and preheat oven to 400 degrees. In a large bowl, whisk together the all-purpose flour, cake flour, sugar, baking soda, cream of tartar and salt. Cut 2 Tablespoons of cold butter into chunks and add to the flour mixture. Using your clean hands, work the butter into the dry ingredients until it is completely incorporated. Make a well in the center of the dry ingredients and add 1 1/2 cups of the buttermilk that has been mixed with the orange zest. Use a fork to work the ingredients together. Mix in the raisins. Add up to another 1/4 cup of buttermilk, adding 1 Tablespoon at a time, until a dough forms.
Turn out onto a lightly floured surface and pat together to form a 6'' round. Place dough into an 8'' inch (or large) cast-iron skillet. If you don't have a cast-iron skillet you can use a baking sheet, but the outside won't get as crispy. Use a sharp knife and cut an "x" into the top of the loaf, about 5-inches long and 3/4-inch deep. Bake for 40 minutes. Remove from oven and brush with 1 Tablespoon of melted butter. Cool for a few minutes, slice and serve. Best if eaten on the day it is made.