Step1
Preheat your oven and prepare the cake batters as described on the store bought cake mix. Pour the batter into all three pans: the two round 9 inch pans and the square 8 inch pan. Bake as directed and wait for the cakes to completely cool. This could take a couple hours after they are done baking.
Step2
Slide a knife around the edge of the round pans to release any cake sticking to the sides. Turn the cake over and gently remove it from it's pan. Place one of the round cakes on your cake platter to begin decorating.
Step3
Open a can of frosting and apply a thin layer to the top of the cake. This will act like glue because the other round cake will sit right on top.
Step4
Remove the second round cake from it's pan like you removed the first. Center it on top of the first round cake. Use your frosting again to frost the entire 2 cakes together. Make the finish as smooth as possible.
Step5
Run your frosting knife under hot water and gently smooth the edges of the frosting. This will help make the frosting extra smooth for decorating later.
Step6
Remove the square cake from it's pan the same way you removed the round cakes. Cut 1 inch off of 1 of the square sides. Then, Cut 1 inch from 1 of the adjacent sides. Now you have a 7 inch square cake. Center the cake on top of the 2 round, frosted cakes.
Step7
Frost the square cake the same way you frosted the round cakes. Be sure to include step 5 while frosting.
Step8
Place the entire cake into the refrigerator for 1 hour to allow the frosting to set. It will be much easier to decorate on top of firm frosting. While you are waiting for the cake to set, get out 4 ice cream cones.
Step9
Frost the outside of the ice cream cones. Once the cake has been in the fridge for 1 hour, remove it and place back on the counter. Place 1 ice cream cone upside down on top of the round cake and beside one of the square cake sides. Place 2 more ice cream cones beside 2 different sides of the square cake. The side of the square that does not have a tower will be the front of your castle. Finish by centering one more upside down frosted ice cream on the top of the square cake.
Step10
Draw a line 2 1/2 inches long on your piece of paper. Then, on one end of the line, draw a 1 inch line perpendicular to it. Connect the other end of the 1 inch line to the other inch of the 2 1/2 line to make a triangle. This will be your tower flag. Repeat the drawing 3 more times and cut them out with your scissors.
Step11
Pick up your tube of decorating icing and edge with bottom of the cake with a continuous line. Then, line where the square cake and the round cake meets. Edge around each tower as well. This decorating frosting will act like the glue that holds the towers in place. Also place a dot of the decorating frosting on the top tips of the towers.
Step12
Create doors and windows on your castle with your tube of decorating frosting. You can easily make these by drawing upside down horseshoe shapes and filling them in.
Step13
Tape your triangle flags to the end of 4 toothpicks. Stick 2/3 of each toothpick into the top of each tower. This is the finishing touch.