In a medium-to-large bowl, combine flour, sugar, and baking powder. Cut in butter until mixture is crumbly. Stir in currants, lemon zest and lemon juice. Beat egg with half and half and add to dry ingredients, stirring until blended. Turn dough onto a lightly floured surface and form into a large circle, 3/4 to 1-inch in thickness. Cut into 8-10 wedges (depending on desired size) and place on lightly greased baking sheet. Brush scones with a beaten egg or egg-milk mixture for a nice finish, and bake at 375° for 10-15 minutes or until golden brown.