These decadent treats are made with crunchy chocolate, walnut, and brown sugar shortbread cookies and a generous layer of creamy walnut frosting. Shortbread cookies are typically sweetened with powdered sugar, but I used turbinado, a coarse variety of brown sugar, instead. For the frosting, I adapted an excellent recipe from the blog Cake Decorist, adding sea salt and reducing the sugar to let the walnut flavor shine through.
Chocolate Walnut Sandwich Cookies
½ cup unsalted butter, softened at room temperature
½ cup turbinado or brown sugar
3 tablespoons cocoa powder
¼ teaspoon salt
1 cup all-purpose flour
¼ cup finely ground walnuts
Adapted from Cake Decorist’s Amazing Walnut Buttercream Frosting
1/2 cup unsalted butter, softened at room temperature
2 cups powdered sugar
1/4 cup walnuts, finely ground
1 tablespoon whole milk or almond milk
1/4 teaspoon salt
Prepare the cookies: Preheat oven to 325 degrees F and line a baking sheet with parchment paper or a silicone baking mat. In a large bowl, cream together butter and sugar until fluffy. Stir in salt, cocoa powder, and walnuts, then mix in flour until just incorporated. Shape dough into a disc and refrigerate until no longer sticky; for maximum flavor, refrigerate overnight. On a lightly floured work surface, roll out dough until around 1/4 inch thick. Shape with a round 2-inch cookie cutter, or other shapes/sizes, if desired, and transfer to baking sheet. Bake for around 12-15 minutes (longer, if making larger cookies) until firm. If unsure when the cookies are done, err on the side of under-baking. Let cool for a few minutes on baking sheet before transferring to cooling rack. If you think you took the cookies out a little early, let them cool fully on the baking sheet.
Prepare the frosting and assemble: In a large bowl, cream together butter and sugar with a handheld electric mixer, or with a wooden spoon, until light and fluffy. Beat or stir in walnuts, milk, and salt until well-incorporated. If preparing in advance, refrigerate until ready to use. Spread a generous layer of frosting on half the cookies (I turned the cookies upside down before frosting them) and then top with the remaining cookies to form sandwiches. Serve right away, or store in the refrigerator.
Yields around 11-12 sandwich cookies