Note: To make gray icing, add a little black color to white icing.
In advance, cover Key Pattern with waxed paper. Outline pattern with tip 2 and full-strength color flow. Flow in with thinned color flow in cut parchment bag. Make 12 keys (make extras to allow for breakage); let dry.
Place car cake on board; ice windows and windshield smooth with spatula. Outline windows and doors with tip 4. Cover body of car with tip 16 stars. Pipe-in front and back lights with tip 8 (smooth with finger dipped in cornstarch). Pipe tip 21 tires and tip 8 dot wheel covers; pipe tip 12 bumpers and running boards. Outline tip 4 steering wheel. Pipe tip 12 ball head (smooth with finger dipped in cornstarch). Pipe tip 2 string hair and facial features. Pipe tip 8 outline arms and tip 2 dot hands and fingers.
Bake and cool two 1 1/2 in. layers to form one 3 in. high cake; prepare for
stacked construction. Ice smooth. Add tip 21 star top and bottom borders. Position car cake. Attach keys with dots of icing. Print tip 4 message.
The star tip creates the most celebrated, easily accomplished decorations! The serrated edges of the star tip make ridges in the icing as you squeeze it out. Because fill in requires so much piping from the same bag, keep replenishing icing in bag.