Combine flour, sugars, salt and baking powder in a large bowl and mix well. Stir in melted chocolate, orange zest and juice, vanilla, egg whites and white chocolate and continue mixing. Knead dough with your hands until mixed thoroughly, dough will be stiff. Separate dough into 4 equal pieces and roll out to form 4 log shapes that are about 2 inches thick and 12 inches long. Preheat oven to 350F. Place logs on a lightly greased baking sheet and bake for 20 minutes. Allow to cool completely. Reduce heat of oven to 300F. Slice logs into 1/2-inch pieces and lay them on their sides. Return to the oven for 9 more minutes. Turn over to other side and cook an additional 9 minutes. Cool.