In a medium bowl, cream together the shortening and brown sugar. Stir in the vanilla. Combine the whole wheat flour, all purpose flour, baking powder, baking soda and salt, stir into the creamed mixture alternately with the milk. Cover and chill dough until firm.
Preheat oven to 350 degrees F (175 degrees C). Grease cookie sheets. On a lightly floured surface, roll the dough out to 1/8 inch thickness. Cut into rectangles. Place 1/2 inch apart onto the prepared cookie sheets.
Bake for 10 to 12 minutes in the preheated oven, or until crisp. Edges will be golden brown. Remove from baking sheet to cool on wire racks.