Two days in advance: Make cookies. Prepare cookie dough and roll out 1/8 in. thick. Cut mortarboard using cutter from graduation set. Cut six to eight stars using medium cut-outs from set. Bake and cool cookies separately due to different cookie sizes.
Prepare Color Flow icing. Tint portions yellow, black and blue.
For stars, use tip 2 and full-strength yellow Color Flow icing to outline three to four star cookies. Use tip 2 and full-strength black Color Flow icing to outline the remaining stars. Using a cut parchment bag and thinned Color Flow icing, fill in stars with matching colors. Reserve full-strength Color Flow. Let set until completely dry.
For mortarboard, use tip 3 and full-strength blue Color Flow icing to outline cookie. Let set. Use cut parchment bag and thinned blue Color Flow icing to fill in cookies. Let dry one day.
Use tip 2 and full-strength yellow Color Flow icing and tip 2 to pipe a line from center of hat to side. Use tip 2 and full-strength yellow Color Flow icing to pipe lines for tassel strings. Let set for a few minutes, and then pipe a ball using tip 3 and full-strength yellow Color Flow icing for center ball. Flatten slightly with finger dipped in cornstarch. Let dry for one day.
Attach cookie stick to back of mortarboard cookie with full-strength Color Flow icing.
Individually prepare three boxes white cake mix following package instructions; divide in thirds. In one portion of batter, gently stir in Sky Blue Icing Color to desired shade. (Use clean toothpicks to transfer color from jar to batter.) Repeat with Lemon Yellow Icing color for second portion. Leave third portion white batter.
For bottom layer, place Batter Dividing Ring in the first prepared pan. Pour white batter in outer section, yellow-tinted batter in middle section and blue-tinted batter in center. Fill sections 2/3 full. Remove ring from pan by carefully lifting straight up on handles. Rinse and completely dry ring.
For top layer, place dividing ring in second prepared pan. Pour blue-colored batter in outer section, white batter in middle section and yellow-colored batter in center. Fill sections 2/3 full. Remove ring from pan by carefully lifting straight up on handles. Rinse and completely dry ring.
For middle layer, place clean ring in third prepared pan. Pour yellow-colored batter in outer section, blue-colored batter in middle section and white batter in center. Fill sections 2/3 full. Remove ring from pan by carefully lifting straight up on handles. DO NOT PUT RING IN OVEN.
Bake and cool cakes following recipe directions. Prepare buttercream icing. Tint portions light yellow, medium yellow, black and red; reserve some white. Stack on foil-wrapped cake circle and ice cake smooth with light yellow buttercream icing and spatula.
Divide cake into 12th using Cake Dividing Set. Use diploma cookie cutter from graduation set to imprint two diplomas in each section of cake.
Using tip 3 and black buttercream icing, outline diplomas. Using tip 14 and white buttercream icing, fill in with stars. Using tip 47 and red buttercream icing, pipe stripe ribbon down center of diploma. Using tip 8 and red buttercream icing, pipe bow loops. Pat smooth with finger dipped in cornstarch.
Using tip 17 and black and medium yellow buttercream icing, pipe stars on cake sides. Using tip 16 and light yellow buttercream icing, pipe shell bottom border.
Insert mortarboard in center of cake. Position cookie stars around mortarboard by piping tip 3 icing mounds behind stars for support.
One of the most popular techniques, stars come in a range of sizes and styles. Experiment with open and closed stars for variation in look. The star technique is timeless and can be used as a classic border or as a stunning fill-in for the top of a dessert.