Preheat the oven to 400F. Line a 8-10 inch cast iron skillet with parchment paper.
In a large mixing bowl, add the gluten-free flour blend, granulated sugar, kosher salt, baking powder and baking soda. Whisk until combined.
Add the cold butter to the dry ingredients and mix with a pastry cutter or two knives to cut it into the dry ingredients.
Stir in the currants until evenly distributed.
In a measuring cup add 1 ¼ cups of buttermilk and an egg to a bowl or measuring cup. Whisk until combined.
Make a well in the center of the dry ingredients and add the buttermilk mixture.
Mix with a spatula until the dough comes together. If the dough is still too dry, add additional buttermilk by the tablespoon (up to an additional ¼ cup) to get the dough to combine together into a disk.
Form into a disk about 6-inches in diameter. Don't worry if the disk is scraggly or not smooth.
Transfer the disk to the prepared cast iron pan or a baking sheet. Brush the disk with a tablespoon of buttermilk.
Use a knife to cut a deep cross or "X" into the top of the dough.
Bake at 400F for 30-40 minutes, until golden brown and a toothpick or skewer inserted into the center comes out clean.
Let cool for about 10 minutes on the pan before removing to a wire rack to continue cooling.
Allow to finish cooling completely. Slice and serve warm with Irish butter.