In a large mixing bowl, combine flour, sugar, baking soda, baking powder and salt. Cut in butter with a pastry blender or fork, until mixture resembles coarse meal. Stir in caraway seeds and raisins or currants.
In a separate bowl, whisk together buttermilk and egg whites, stir into flour mixture until moistened.
Turn out onto a well floured surface and knead lightly until smooth. Shape dough into a ball and place in a 7-inch round loaf pan. Cut a 4-inch cross about 1/4-inch deep on top with a serrated knife. Brush top with milk.
Bake for 1 hour or until golden brown. Cool on a baking rack. Serve warm with butter.