Preheat the oven to 375°F. If you wish, line the skillet with parchment paper. However, you can skip this step if you prefer.
In a large bowl, whisk together the flour, baking soda, sugar, baking powder and salt. Create a well in the center and pour in the buttermilk. Slowly stir with a wooden spoon, scraping down the sides as it becomes a sticky dough (see notes below).
Dust a work surface generously (use about 1/4 cup) with flour. Dump the dough onto the surface and with floured hands, gently and quickly knead the dough into a round. Use a sharp knife to cut a cross in the dough, but do not cut all the way through. Use a bench scraper to carefully transfer the dough into your skillet.
Bake for about 20-30 minutes, or until the bread is golden and makes a hollow sound when tapped. The bread will be fully cooked and fluffy on the inside. Remove the skillet from the oven and let it cool for about 30-45 minutes on a wire rack, with a kitchen towel draped on top.
The dough will be very sticky; I have received comments saying that the dough is thin like cake batter. That should not be the case -- the quality of your buttermilk will really make a difference here. Do not substitute with "buttermilk" made with milk and vinegar or lemon juice, as that will be too thin. You will want to use a good quality, thick buttermilk. If you still feel that the dough is too sticky, simply add a little more flour until you get the consistency as the one pictured in the post.Adapted from my mom’s Irish Soda Bread and Irish Soda Farls from the Wall Street Journal.