Preheat oven to 400 degrees. Lightly grease 2 baking sheets. Combine the flour, baking powder, baking soda, and salt. In a large bowl, cream the vegetable shortening and brown sugar. Beat in the egg and sour cream. Gradually blend in the dry ingredients. Fold in the dates. Drop the dough by spoonfuls 4 cm apart onto the prepared baking sheets. Press a walnut into the center of each cookie. Bake for 8 to 10 minutes, until lightly colored. Transfer to wire rack to cool. ----