Bake and cool cookies (2 for each sandwich) according to recipe instructions.
Dilute icing colors with vanilla extract and use brush to paint colors on pumpkin on top cookie. Pipe tip 3 line of royal icing around rims of cookies and roll in Halloween Nonpareils; let completely dry.
Just before serving, use round cutter from set to cut a 1/2 in. thick slice of ice cream and position between cookies.