Combine flour, sugar, baking powder, and salt; cut in butter with a pastry blender until mixture resembles coarse meal. Stir in currants. Gradually add enough milk to the mixture to form a soft dough, stirring just until dry ingredients are moistened. Turn dough out onto a lightly floured surface, and knead lightly 4 or 5 times. Roll dough to 1/2-inch thickness; cut with a 2-inch biscuit cutter. Place on lightly greased baking sheets. Bake at 450 degrees for 8 to 10 minutes or until lightly browned. Serve warm.