The secret to Irish Soda Bread lies in baking soda and buttermilk. When combined, they release carbon dioxide which makes the bread rise without yeast.
Preheat oven to 375 degrees. Line a sheet pan with parchment paper. Combine flour, sugar, baking soda, and salt in the bowl of an electric mixer fitted with a paddle attachment. Add butter and mix on low speed until butter is mixed into the flour.
With a fork, lightly beat the buttermilk, egg, and orange zest together in a measuring cup. With mixer on low speed, slowly add buttermilk mixture to flour mixture.
In a small bowl, mix currants with 1 tablespoon of flour, then mix into the dough. Dough will be very wet.
Turn the dough out onto a well-floured board and knead a few times into a round loaf. Place the loaf on prepared sheet pan and lightly cut an X into the top of the bread with serrated knife.
Bake for 45- 55 minutes, or until a toothpick or wooden skewer comes out clean. When you tap the loaf, it will have a hollow "thump" sound. Cool on a baking rack. Serve warm or at room temperature.
Notes
Sugar: For a less-sweet Irish soda bread, reduce sugar to 2 or 3 tablespoons.