Amaze your family with these double chocolate delight cookies filled with creamy vanilla frosting that can be prepared in less than 30 minutes.
Line 2 sheet pans with parchment. Heat oven to 350°.
Combine flour, brown sugar, cocoa powder, baking soda and salt in a medium-size bowl. Whisk to blend. Stir in buttermilk, egg and melted butter. Stir with a wooden spoon until just blended.
Spoon some of the mixture into a large resealable plastic bag. Snip a 1/2-inch corner from the bag. Pipe 3-1/2 x 1-inch logs, about 2 inches apart, on prepared pan, about 12 per pan. Bake until firm to the touch, 12 to 14 minutes. Transfer to wire rack and let cool completely.
Spoon the frosting into a second resealable bag. Snip a 1/2-inch corner from the bag. Pipe some of the frosting onto the flat side of half of the cookies. Sandwich with another cookie, flat side against frosting. Continue with remaining cookies and frosting.