Preheat the oven to 375 degrees F. Line a sheet pan with parchment paper or a Silpat baking mat.
Combine the flour, sugar, baking soda, and salt in the bowl of an electric mixer fitted with the paddle attachment.
Add the butter to the mixer and blend on low speed until the butter is the size of peas. Don’t overmix.
In a separate bowl, lightly beat the buttermilk and the egg together.
With the mixer on low speed, slowly add the buttermilk and egg mixture to the flour mixture.
Coat the currants or raisins with 1 tablespoon flour and mix them into the dough.
Dump the wet dough onto a well-floured board. Knead lightly until just smooth, about 1 minute. Form the dough into a ball and place it on the center of the prepared baking sheet. Using a serrated knife, cut a ¼” deep “ X” into the top of the bread.
Bake 45 to 55 minutes, until well browned and the bottom sounds hollow when tapped lightly with your knuckles.
Cool on a baking rack for at least 15 minutes. Serve warm or at room temperature, slathered in butter.
For a savory version, omit the fruit and zest and add 1 tablespoon caraway seeds, fennel seeds, or dried dill