In a large bowl, whisk together the flour, white sugar, salt and baking powder until well combined.
Use a pastry cutter or large fork to incorporate the cold butter into the flour mixture until well-distributed and dry ingredients resemble clumpy sand.
Stir in the raisins and set aside.
In a small bowl or large measuring cup, beat together the buttermilk and egg until well-combined.
Make a well in the center of the dry ingredients and pour in the milk-egg mixture. Stir the wet ingredients into the dry ingredients until you're unable to stir anymore, then use your hands to continue kneading the dough, at least 2 minutes until no longer sticky and the dough forms a cohesive ball.
Place the ball of dough onto the prepared skillet or cookie sheet.
Use a sharp knife to cut a large X-shape in the center of the dough to allow steam to escape.
Bake for 45-55 minutes, until golden brown and an inserted toothpick comes out clean.
Notes
Avoid the desire to add more flour to the dough for at least a minute - it will be sticky at first but should become less sticky with kneading.