01 - Boil the quartered potatoes in lightly salted water until they are fork-tender, which typically takes about 15 minutes. Thoroughly drain the cooked potatoes and return them to the hot pot to allow any residual moisture to steam off.
02 - While the potatoes are still warm, mash them completely until they are smooth and free of any lumps.
03 - Add the 3.5 tablespoons of unsalted butter and whole milk to the mashed potatoes, mixing thoroughly until well combined.
04 - In a separate large mixing bowl, combine the all-purpose flour, fine sea salt, and baking powder. Gradually add the warm potato mixture to the dry ingredients and gently mix to form a soft, cohesive dough.
05 - Transfer the dough to a lightly floured surface. Knead briefly until smooth, then pat or roll the dough out to approximately 1/2 inch thickness. Cut the dough into 8 equal triangles or rounds.
06 - Heat a non-stick skillet or griddle over medium heat. Cook the shaped bread slices in batches for about 3–4 minutes per side, until they achieve a golden-brown color and a crisp texture.
07 - Serve the Irish potato bread immediately, generously spread with additional butter.