Preheat the oven to 190°C. Line a sheet pan with parchment paper.
Combine the flour, sugar, baking soda, and salt in the bowl of an electric mixer fitted with the paddle attachment. Add the butter and mix on low speed until the butter is mixed into the flour.
With a fork, lightly beat the buttermilk, egg, and orange zest together in a measuring cup. With the mixer on low speed, slowly add the buttermilk mixture to the flour mixture. Combine the currants with one tablespoon of flour and mix into the dough. It will be very wet.
Dump the dough onto a well-floured board and knead it a few times into a round loaf. Place the loaf on the prepared sheet pan and lightly cut an X into the top of the bread with a serrated knife. Bake for 45 to 55 minutes, or until a cake tester comes out clean. When you tap the loaf, it will have a hollow sound.
Cool on a baking rack. Serve warm or at room temperature.