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