1. In a large bowl, combine the flours, brown sugar, and baking soda, and stir to mix well. Add the Prune Puree, honey, and vanilla extract, and stir to mix well. (Note that the dough will seem dry at first. Keep stirring until it holds together.) Fold in the mint chocolate chips and, if desired, the walnuts.
2. Coat a baking sheet with nonstick cooking spray. Drop rounded teaspoonfuls of dough onto the baking sheet, placing them 1 1/2 inches apart. Slightly flatten each cookie with the tip of a spoon.
3. Bake at 350°F for 9 to 10 minutes, or until lightly browned. Cool the cookies on the pan for 1 minute. Then transfer the cookies to wire racks, and cool completely.