Preheat your oven to 400 degrees. Line a baking sheet with parchment paper and set aside.
In a small bowl whisk together the buttermilk and egg. Set aside.
Mix the flour, sugar, baking soda and salt together in a bowl and lightly mix together. Add the currants and orange zest if using and lightly coat with the flour mixture.
Grate the cold butter directly into the mixture or cut the butter into small chunks or use a pastry cutter until the butter is finely incorporated. There should be no big lumps of butter, just small pea-sized pieces.
Pour the buttermilk mixture into the flour mixture and stir to lightly incorporate. If the dough is a little sticky, add a little extra flour. Turn the dough out onto the counter and knead once or twice. This is a quick bread, so you don’t want to activate the gluten in the flour with a lot of kneading. Shape into a round circle.
Transfer the loaf to the baking pan and score a large X on the top. Bake for 20 minutes and then check the top of your bread. If it is browning quickly, cover the top with a sheet of aluminum foil to prevent burning. Bake until the bread is cooked through, about 45-50 minutes.
Allow bread to cool 15 minutes and then serve warm. It can also be eaten at room temperature or toasted for a snack later. Enjoy!