To make paintbrush, work the flour into the cookie dough until smooth. Roll dough out on foil to a 1/4-inch thickness; cut out handle shape. Transfer cutout (on foil) to baking sheet. Bake until golden brown, 8 to 10 minutes. Transfer to wire rack and cool completely. For bristles, cut 2 pieces of licorice in half lengthwise, then in thirds crosswise (for a total of 12 pieces). Spread a small amount of vanilla frosting along straight side of cookie handle and press twist pieces into frosting. Secure with a 3/4" strip of foil. Set aside to dry.