Preheat the oven to 375° F. Line a sheet pan with parchment paper.
Combine the flour, sugar, baking soda, and salt in the bowl of an electric mixer. Using the paddle, 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, slowly add the buttermilk mixture to the flour mixture. Combine the currants with 1 tablespoon of flour and mix into the dough. The dough will be fairly wet.
Dump the dough onto a well-floured board and knead it a few times. Form into a round loaf.
Place the load on the prepared sheet pan and lightly cut with a X into the top of the bread. Dust with a little flour.
Bake for 45 - 55 minutes or until a cake test comes out clean. The loaf should have a hollow sound when tapped on the bottom.
Cool on a baking rack. Serve warm or at room temperature.