Preheat oven to 375 degrees. In a mixer, cream margarine and sugar. Add baking powder, eggs, yolk and soymilk and mix well. Beat in cocoa and flour. Stir in chocolate chips and nuts, if using.

Divide dough in half and shape into logs. Place on lightly greased cookie sheet. Combine egg white and water and brush on top of logs. Sprinkle with sugar. Bake for 25 minutes or until lightly toasted. Cool slightly. Slice and return to oven for about 10 minutes. Cool on wire rack.