01 - Preheat the oven to 425°F. Line a baking sheet with parchment paper.
02 - In a large mixing bowl, whisk together the flour, baking soda, salt, and sugar (if using).
03 - Create a well in the center and pour in most of the buttermilk. Mix gently with your hand or a wooden spoon until a soft dough forms, adding additional buttermilk if necessary.
04 - Turn the dough onto a lightly floured surface. Knead briefly for approximately 30 seconds just to bring it together—avoid overworking. Shape into a round loaf about 2 inches thick and place on the prepared baking sheet.
05 - Cut a deep cross (X) on top of the loaf with a sharp knife. Bake for 35 to 40 minutes until golden brown and the loaf sounds hollow when tapped on the bottom.
06 - Transfer to a wire rack and cool for at least 10 minutes. Serve warm, thickly sliced with generous spreads of Irish butter.