Add the butter to the flour and seed mixture. Using just your fingertips, rub the butter into the flour until it resembles coarse crumbs.
2 tablespoons softened butter
In another bowl or measuring cup, lightly whisk the egg together with the buttermilk.
1 egg, 1 ⅔ cups buttermilk
Make a well in the center of the flour and butter mixture and pour in approximately 3/4 of the buttermilk and egg mixture. Using your hand, bring the dry and wet ingredients together. Work in a circular motion beginning in the center and bringing in flour from the sides of the bowl. Add more of the buttermilk if needed to make a soft but not sticky dough.
Lightly flour your work surface and turn the dough out. Gently shape the dough into a round about 1 1/2 inches thick.
Transfer to a baking sheet. Cut a deep cross in the top of the dough round and prick each quadrant with the point of a sharp knife.
Bake for 15 minutes. Turn the oven down to 400 degrees and continue baking for an additional 30 minutes.
To test whether the loaf is done, tap it on the bottom. If it sounds hollow, it’s ready.
Place on a wire rack to cool.
Notes
Irish soda bread is meant to be eaten on the same day it’s baked. However, if you do have leftovers, store the completely cooled loaf wrapped tightly in plastic wrap or aluminum foil at room temperature for up to two days.
Avoid refrigerating the bread, as this can dry it out quickly.
To reheat, warm individual slices lightly in a toaster or briefly in a moderate oven until just heated through.