Crank your oven to 425°F and butter a 9-inch round cake pan well. The high initial temperature creates the crust you want on this bread.
Combine the flour, salt, baking soda, and sugar in a large bowl, whisking them together until evenly distributed. These dry ingredients need to be perfectly mixed before you add anything wet.
Work the cold butter cubes into the flour mixture with a pastry cutter or your fingertips until you get coarse, uneven crumbs. Some larger pieces are fine — you want texture, not uniformity.
Whisk the Guinness, buttermilk, and beaten egg together in a separate bowl until smooth. The stout should be at room temperature so it doesn't shock the other ingredients.
Add the wet mixture to the flour mixture and fold together with a wooden spoon just until a shaggy dough forms. Stop the moment it comes together — overworking will make your bread tough and dense.
Dump the dough onto a lightly floured counter and gently pat it into a round loaf that fits your prepared pan. Handle it as little as possible while still getting a decent shape.
Score a deep X across the entire top with your sharpest knife, cutting about halfway down into the loaf. This classic mark helps the bread bake evenly and looks properly traditional.
Slide the pan into the oven for 15 minutes, then drop the temperature to 400°F and continue baking for 30 minutes more. The finished loaf should be deep golden and sound hollow when you tap the bottom.
⏱ 45 min
Let the bread rest in the pan for 10 minutes before turning it out onto a cooling rack. This brief rest prevents it from falling apart when you remove it.
⏱ 10 min