***All of these steps can be done one day before assembling and frosting the cake.***
Preheat oven to 350° F.
Pour 2-½ cups of cake batter into the small prepared cake pan and 5-½ cups of cake batter in the large prepared cake pan. The pans should be about ⅔ full. Bake for 25 to 30 minutes. Test for doneness and remove pans from oven. Allow cakes to sit in pans for 10 minutes, then remove each and allow to cool completely on a wire rack. Don't try to frost or trim the cake while it's hot, or it will disintegrate.
Frosting (make 2 batches)
Cream butter and shortening in the work bowl of the mixer. Add vanilla and mix for about 30 seconds. Gradually add sugar, one cup at a time, beating well on medium speed and scraping the sides and bottom of the bowl. Add the milk and beat at medium speed until light and fluffy. Keep the frosting covered with a damp cloth so that it doesn't dry out.
Prep the freezer bags for piping. Put the base of a coupler in the bottom corner of a bag and cut away the corner. Add a #3 or #12 tip and screw the coupler ring over the bag and tip. Fill with frosting, squeeze any extra air out of the bag, and twist the top.
Yellow Frosting: Put 2 tablespoons of frosting into a small bowl. Squeeze a few drops of yellow coloring into the frosting and stir with a popsicle stick. Start with a small amount of color and add more as needed until you have a bright yellow. Put all of the yellow into the freezer bag with the #12 tip.
Blue Frosting: Put 2 cups of frosting into a small bowl. Squeeze a few drops of blue coloring into the frosting and stir with a popsicle stick. Start with a small amount of color and add more as needed until you have sky blue. Put about ½ cup of the blue into a freezer bag with the #3 tip.
Red Frosting: Put the remaining frosting in another small bowl. Squirt 20 to 30 drops of the liquid red food coloring into the frosting and stir. This gives the color a good strong pink base to work from. Start adding the No Taste gel coloring a little at a time, stirring as you go until you have a deep bright red. Put about ½ cup of the red into a freezer bag with the #3 tip.
Cakes: Level the tops of the cake as necessary using a serrated bread knife or a cake leveler. Place the large cake layer on the plate. Lay the small cake layer on top of the large layer with the ends of the ovals aligned. Position the end of the top layer approximately ½ inch away from the end of the bottom layer. This will be the back end of Rocket. Use the serrated bread knife to trim the back end of the top layer so that it slopes down toward the bottom layer. Trim the top edges of both layers to round them a little. Take the spare trimmings and lay it on top of the top layer. Shape with your hands and knife to make a rounded top.
Use a spatula to cover the top and sides of the bottom layer with the red frosting.
Cover the sides of the middle layer with the blue frosting.
Cover the rounded top layer with red frosting.
To make the headlights, pipe some yellow frosting into two small circles on the front of the bottom layer.
Pipe the red frames on the blue windows and detail lines around all edges on each layer. Pipe 5 vertical lines on the bottom layer, one in the front center, and two more on each side, evenly spaced around the cake. Pipe one line on the top layer from front to back. Pipe a circle of frosting on the very top of the cake and then insert the lollipop, leaving about 1 inch of stick visible.
Make the Engines: Set aside 2 of the ice cream cones. Using the X-Acto knife, cut away the bottoms of the other 4 ice cream cones, saving the tops and 2 of the bottoms. If the cones have a flared top edge, cut that away on the two rings but not on the uncut cone. Set aside two of the cone bottoms. Take the four "rings" and cut a groove in each about the width of a graham cracker. Take 2 graham cracker squares and trim each so that it's shaped like a fin.
To assemble the engines, insert a bottom cone piece into an uncut cone leaving the bottom hanging out. Position two rings around the bottom of that cone with the cut grooves aligned, and then insert the graham cracker fin into the grooves.
Frost the engines using red on the top fin, the outsides of the engines , and on the front part of the engine that sticks out. Pipe some blue frosting in the cavity between the outside edges and the inside cone. Pipe some blue frosting on the back of the engine (the exhaust). Pipe red detail lines on the sides and around the base of the fins.
Attach the Engines: To finish the cake, lay the frosted engines on the plate next to the back of the cake and connect them using a chopstick that runs through the cake. Find the approximate horizontal center of the engine and use the X-Acto knife to drill a hole through it about the diameter of the chopstick. Insert the chopstick through the back of the cake, running one side to the other. Gently push each engine onto the chopstick through the holes you drilled. Pipe some red frosting onto the chopstick to fill in the area between the cake and the engine.