Step 1: Preheat your oven to 425°F (218°C) and line a baking sheet with parchment paper or lightly grease a cast-iron skillet.
Step 2: In a large mixing bowl, whisk together the flour, sugar, salt, and baking soda until well combined.
Step 3: Add the cold, cubed butter to the dry ingredients. Use your fingers or a pastry cutter to work the butter in until the mixture looks like coarse crumbs.
Step 4: Make a well in the center of the mixture and pour in the buttermilk. Stir gently with a wooden spoon until a shaggy dough forms.
Step 5: Turn the dough out onto a lightly floured surface. Gently knead it just 4-5 times to bring it into a cohesive ball. Do not over-knead.
Step 6: Shape the dough into a round loaf, about 1.5 to 2 inches thick. Place it on the prepared baking sheet.
Step 7: Use a sharp knife to score a deep 'X' into the top of the loaf, about an inch deep.
Step 8: Bake for 35-40 minutes, or until the loaf is golden brown and sounds hollow when tapped on the bottom. Let cool on a wire rack before slicing.