Preheat the oven to 375°F. Line a large baking sheet with parchment paper and set aside.

In the bowl of a stand mixer fitted with the paddle attachment, add the flour, sugar, baking soda, and salt. Stir to combine.

Measure the buttermilk into a 2-cup liquid measuring cup. Add the egg and whisk them together with a fork. Add the orange zest to the cup and set aside.

Keep the butter in the fridge until you are ready to work with it. Cut the butter into small cubes and add it to the stand mixer.

Mix the butter into the flour on low speed until it has been completely incorporated in the mixture.

Slowly add the reserved buttermilk to the mixing bowl and continue to mix on low speed until the dough forms.

Sprinkle the reserved 1 tablespoon of flour over the raisins or currants in a small mixing bowl. Toss to coat, this will help them to not sink to the bottom of the dough while it bakes.

Add the raisins or currants to the mixer and stir to combine, the dough will be very wet.

Transfer the dough to a lightly floured baking mat. Knead it by hand a few times and form a round-shaped loaf. Transfer the dough round to the prepared baking pan and slice an X over the top.

Bake for 55 minutes - 1 hour or until a cake tester inserted in the center comes out clean. The soda bread will sound hollow when you tap on it.

NOTE: If the bread starts to darken too much before the baking time is over, you may lightly cover it with aluminum foil.