Preheat your oven to 425°F (220°C).
In a large mixing bowl, whisk together the flour, baking soda, and salt.
Make a well in the center of the dry ingredients and pour in the buttermilk.
If using, fold in the raisins or currants until just combined.
Turn the dough out onto a floured surface and knead gently for a few seconds.
Shape the dough into a round loaf and place it on a baking sheet lined with parchment paper.
Using a sharp knife, score a deep cross in the center of the dough.
Bake for 30-35 minutes until golden brown.
Let the bread cool on a wire rack for at least 10 minutes before slicing.