Preheat your oven to 425 degrees. Spray a 9-inch round cake pan with nonstick cooking spray. Set the pan aside.
Place a fine-mesh sieve over a large bowl. Sift in the flour, baking soda, and salt.
Pour the buttermilk into the large bowl containing the dry ingredients. Mix with a silicone spatula until a dough forms.
Transfer the dough to a floured surface. Gently knead the dough into a smooth, round shape. Avoid overworking the dough, since this will affect the density.
Place the rounded dough ball into the prepared cake pan. Carefully spread the dough toward the edges of the pan with your fingers. The dough should cover most of the bottom of the pan.
Cut a deep X across the top of the dough.
Bake uncovered for 35 minutes or until the top of the bread is golden brown and a toothpick inserted into the center comes out clean.
Allow the soda bread to cool for 5-10 minutes before transferring it to a wire cooling rack to cool completely. Serve the bread with butter.
Irish soda bread can be stored in an airtight container for 3-5 days.