Preheat the oven to 400°F / 205°C and line a baking sheet with parchment paper.
Whisk 4¼ cups of all-purpose flour, 3 tablespoons of granulated sugar, 1 teaspoon of baking soda, and 1 teaspoon of salt. Cut in 5 tablespoons of cold cubed unsalted butter to pea-sized crumbs.
Stir in 1¾ cups of buttermilk until the dough is too stiff to stir. Turn out onto a lightly floured surface, knead for about 30 seconds, and shape into a ball.
Place on the baking sheet and score an X about ½in / 1cm deep. Bake for 45-55 minutes, until a thermometer in the center reads 195°F / 90°C, tenting with foil if it browns too quickly.
