Begin by preheating your oven to 400°F and lightly greasing a baking sheet. In a large bowl, combine the dry ingredients: 3½ cups (450g) bread flour, 1 tsp baking soda, and 1 tsp salt.
Mix these together thoroughly to guarantee the baking soda is evenly distributed throughout the flour. This step is essential as it helps the leavening agent work uniformly when it comes into contact with the wet ingredients.
Add 1 cup + 3 tbsps (300ml) buttermilk (or the milk and Greek yogurt mixture) to the dry ingredients along with about 6 tbsps warm water, adding the water gradually as needed.
Mix until you form a very soft dough—the consistency should be softer than typical bread dough but not so wet that it becomes sticky and unmanageable.
Turn the dough out onto a lightly floured work surface and gently shape it into a neat round about 7 inches in diameter, handling it as little as possible to keep the crumb tender.
Place the shaped dough on your prepared baking sheet and use a sharp knife to make a shallow cross in the top of the loaf. This traditional scoring serves both a practical and symbolic purpose.
Bake for 30 minutes, then carefully turn the bread upside-down and continue baking for an additional 10–15 minutes, or until the bread sounds hollow when tapped on the bottom. Transfer the finished loaf to a wire rack to cool completely before slicing.