Preheat oven to 375 degrees F.

Beat brown sugar, butter, peanut butter and cinnamon in a large bowl with an electric mixer on medium speed until well mixed. Add egg and vanilla; continue beating until well mixed. Reduce speed to low. Add flour, baking powder, baking soda and salt; beat until well mixed, scraping the sides of the bowl as necessary. Stir in dates and walnuts. Refrigerate the dough for at least 1 hour before baking.

Use a small scoop (1 3/8- to 1 1/2-inch) and drop balls of dough 2 inches apart onto an ungreased baking sheet. (If you do not have a scoop, shape the dough by hand into 1- to 1 1/4-inch balls.) Gently press each ball to flatten slightly.

Bake the cookies until the edges are lightly browned, 8 to 10 minutes. Transfer to a wire rack to cool completely.

To decorate: Place white chocolate and oil in a small microwave-safe bowl and microwave on Medium, stirring every 30 seconds, until the chocolate is melted and smooth. To drizzle, dip a fork in the chocolate then wave it over a cookie to create a lacy finish (see Variations). Let the chocolate set for at least 1 hour. Variations: Instead of drizzling, dip the top side of the cooled cookies in melted white or dark chocolate and sprinkle with chopped walnuts.

Tip: Most brands of white chocolate chips are actually not white chocolate at all; they're called "white morsels" and contain no chocolate. We like Sunspire (made without partially hydrogenated oil), found in natural-foods stores or online at sunspire.com, and the Albertsons/ Shaw's store brand, Essensia. Eight ounces chopped pure white chocolate can be used in place of the chips.

MAKE AHEAD TIP: Prepare the dough (Step 2), cover and refrigerate for up to 1 day. Store the cookies in an airtight container at room temperature for up to 3 days.