1. Heat the oven to 400°. Butter a 9-by-5-inch loaf pan. In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt. Cut or rub in the butter until the mixture is the texture of fine meal. Stir in the raisins and caraway seeds.
2. In a medium bowl, whisk two of the eggs to combine. Whisk in the buttermilk. Pour the buttermilk mixture into the dry ingredients and stir until just combined. Put the dough on a floured work surface, pat into a loaf, and put into the prepared pan. Beat the final egg to mix and brush the top of the loaf with it. Using a sharp knife, cut a 1/4-inch-deep lengthwise slash down the middle of the loaf leaving a 1-inch margin at either end.
3. Bake the soda bread in the middle of the oven until well browned and a toothpick inserted in the center comes out clean, 1 hour to 1 hour and 10 minutes. Turn the loaf out onto a rack and let cool. Serve warm or at room temperature.