Preheat the oven to 400°F/200°C. Line a baking sheet with parchment paper. Set aside.
In a large bowl, whisk together flour, sugar, baking soda, and salt. Add the butter into the flour mixture and mix it with your fingers (or a fork/spatula) until butter is evenly distributed. Add buttermilk and mix until a shaggy, slightly moist dough forms. If dough is too crumbly, add more buttermilk as needed (you’ll need no more than 1-2 tablespoons). Don’t overmix.
Transfer dough to a floured surface and knead gently just for a few seconds until a ball forms and it’s cohesive but still lumpy - it shouldn’t look pretty or smooth. You don’t want to overwork the dough, as this can make it tough.
Form dough into a 7-inch round loaf and transfer to prepared pan. Score a deep “X” into the top of the dough. Sprinkle with oatmeal if you like. Bake for 40-45 minutes (If you have a thermometer, the internal temperature should be around 180°F). Transfer to a wire rack and allow to cool to room temperature. Serve warm or at room temperature.
Store bread in an airtight container for up to 2 days. You can also freeze the loaf or cut into slices and then freeze. Thaw in the refrigerator (overnight) or at room temperature.