Preheat the oven to 425°F and dust a baking sheet with flour.

Whisk the flour, baking soda, and salt together in a large bowl.

Make a well in the center and pour in the buttermilk, stirring just until a shaggy dough comes together, adding a splash more buttermilk if dry bits remain at the bottom of the bowl.

If using raisins, fold them in now.

Turn the dough onto a floured surface and knead it gently 4 or 5 times, just enough to bring it together, overworking makes the loaf tough.

Shape the dough into a round about 7 inches across and set it on the baking sheet.

Cut a deep cross into the top with a sharp knife, about 1/2 inch deep, cutting almost to the edges of the loaf.

Bake for 35 to 40 minutes, until the crust is deep golden brown and the loaf sounds hollow when you tap the bottom.

Cool on a wire rack at least 20 minutes before slicing, it keeps baking a little on the inside as it cools.