Preheat oven to 450 degrees F with a rack in the middle.

Mix the flour, baking soda, salt, and buttermilk powder if using in a large bowl until fully incorporated.

Add buttermilk or water and incorporate so a thick batter forms. Do not overwork the dough but gently shape it into a round. Pop in a Dutch oven or cast iron skillet. Use a knife to cut a large X on top.

Bake at 450 for 10 minutes, then lower the oven temperature to 400 and bake for about 20 minutes more, until the bread is golden brown and crusty on the outside.

Note: If you don't have buttermilk in any form, use 1 cup water plus 1 tbsp lemon juice or white distilled vinegar.