Preheat the oven to 400°F. Line a baking sheet with a silicone baking mat or parchment paper or grease with nonstick baking spray.
Add the flours, sugar, salt, baking soda and baking powder to a large mixing bowl.
Make a well in the center of the dry ingredients.
Add the buttermilk and and the oil.
Stir just until combined.
Dump the dough out onto a floured surface, and knead just until it comes together.
Shape the dough into a ball.
Transfer the dough to the prepared baking sheet.
Cut a deep cross into the top of the dough.
Bake the bread about 35-40 minutes, or until a wooden toothpick inserted into the center comes out clean.
Let the bread cool on the baking sheet for about 5-10 minutes.
Serve warm or at room temperature.
Notes
Flour: Most traditional Irish brown soda bread recipes call for only whole wheat flour. I've used a combination of whole wheat flour and all-purpose flour to give the bread a softer, less dense texture.
It's key to measure the flour properly to avoid a heavy, dry loaf. The best way to measure flour is to weigh it. If you don't want to weigh the flour, sift or stir it to break the flour up. Then lightly spoon it into a measuring cup and level.