There are lots of soda bread recipes around, but me, I prefer this one from the queen of Irish cooking, Monica Sheridan. Her 1965 book, The Art of Irish Cooking is a classic, right up there with Mastering the Art of French Cooking by Julia Child. Her recipe is about as traditional as you can get, and great for using up that bag of coarse-ground flour your hippie ex-roommate brought to you after his trip to Vermont.
20 ounces (4 cups) stone ground whole wheat flour (an Irish-style flour is ideal)
10 ounces (2 cups) white flour
1 1/2 tsp baking soda
1 1/2 tsp salt
16 ounces (2 cups) buttermilk
Half an hour before you begin, preheat your oven to 425.
In a large bowl or in the bowl of a mixer fitted with a paddle (beater) stir the flours, salt, and baking soda together. Add the buttermilk and continue to stir until everything is moistened, then switch to the dough hook and knead about a minute until you have a soft and slightly sticky ball. Add flour or more buttermilk as necessary to get the right consistency.
Transfer the dough to a lightly floured surface and flatten it out into a circle that’s about 1 1/2 inches thick. Transfer the dough to a parchment-lined baking sheet or a cast iron pan. With a sharp knife, make a cross-shaped slit in the top.
Bake the bread for 25 minutes, then reduce the heat to 350 and bake for 15 minutes more. Cool on a rack a minimum of an hour, ideally up to six hours, before you cut into it.