Preheat the oven to 350 degrees F.
Sift together the flour and baking powder. In a separate bowl, beat the butter until creamy. Add the 1/4 cup sugar, beating until pale and fluffy. Add the eggs, 1 at a time, then add the flour mixture and the buttermilk. Sprinkle the raisins over the dough and gently fold them in. Using an ice-cream scoop, place mounds of dough on a baking sheet and sprinkle with the remaining sugar. Bake for 20 minutes. Serve the scones warm, with softened butter and preserves.