Whisk together flour, sugar, baking powder, and salt in a large bowl. Add ½ cup butter; rub mixture between your fingers until small crumbles form and texture resembles a coarse meal. Add raisins and egg; gently knead until a soft pie dough–like mixture forms. If dough feels dry, add milk, ½ teaspoon at a time, kneading until just incorporated after each addition.
Transfer dough to a lightly floured work surface, and roll to ⅜-inch thickness. Cut dough into rounds using a 2 ¼-inch round cutter, rerolling scraps as needed, until all dough has been cut into rounds.
Melt 1 tablespoon butter in a large cast-iron skillet over medium-low. Working in 3 batches, cook cakes until golden, crisp, and cooked through, 2 to 4 minutes per side. Remove cakes from skillet. Repeat with remaining cakes, wiping skillet clean and adding 1 tablespoon butter between each batch. Sprinkle cakes with additional sugar, and serve warm with softened butter and fruit jam, if desired.
