Step 1: Preheat your oven, according to directions on the cake mix package, and mix up the cake batter according to package directions.
Step 2: Pour about 2/3 of the batter into the oval cake pan, and 1/3 into the round cake pan. Make the cake levels in both cake pans as even as possible. Bake according to the directions.
Step 3: Remove the finished cakes from the oven and let them cool for a few minutes in the pan.
Step 4: Level the cakes with a serrated knife, so they have flat tops. Turn the cakes out onto a rack to finish cooling.
Step 5: While the cakes are cooling wrap a large cake board (or cardboard) with decorative foil.
Step 6: Using the food coloring, color your icing:
Step 7: Color your gum paste by adding food coloring, and then pulling and twisting the gum paste until the color mixes in evenly.throughout the gum paste. Color your paste like so:
Step 8: Divide the yellow gum paste in half, and shape each piece into an oval for the Grinch’s eyes.
Step 9: Flatten out 2 small pieces of black gum paste, each about the size of a penny. These will be the center of the Grinch's eyes. Place these pieces in the center top of the yellow gum paste eyes, or you can put them a little off center so they’ll be closer together when you add the eyes to The Grinch’s face. Set eyes aside.
Step 10: Pinch off a marble-sized piece of black gum paste. Roll it between your fingers to so it becomes long, thin, and round, like a snake. Split the long, thin, snake-like piece into 3 even pieces. 2 of these will be the Grinch's eyebrows. Split the third piece into 2 pieces; these will be the top of the Grinch's smile. Set these pieces aside.
Step 11: Pinch off another marble-sized piece of black gum paste and roll it long and thin, like a snake. This will be the Grinch's smile. Set aside.
Step 12: Shape the remaining black gum paste into the Grinch’s nose. Set the gum paste pieces aside. Eventually the Grinch face will look as shown below:
Step 13: Place a little icing in the center of the cake board (this will serve as glue to hold the cake in place). Once the cakes have cooled place the oval cake (cut-side down) in the center of the horizontal cake board over the icing. The oval should be vertical on the cake board.
Step 14: From your round cake, cut 2 matching crescent moon shaped pieces. These will be the Grinch's cheeks.
Step 15: Place the cheecks on on each side of the oval cake near the bottom, as shown below. Put sage green icing between the cake pieces to hold them in place.
Step 16: Ice the entire cake sage green. Add a second layer of icing if needed.
Step 17: Allow the cake to set for a few minutes to let the icing dry. Once it is dry, use a piece of waxed paper to smooth the icing.
Step 18: Wipe the cake board with a damp cloth to remove any extra icing.
Step 19: Add the Grinch’s gum paste eyes, nose, mouth, and eyebrows to the cake.
Step 20 (optional): Fill a pastry bag with the leftover green icing. Attach a small round tip to the pastry bag to pipe 2 wrinkles above each eye with the green icing.
Step 21: Add a Santa hat to the top of the Grinch’s head with the red icing. Ice the top 1/4 of the cake with red icing, and let the icing flow over onto the cake board for the top of his hat. Smooth the icing with the wax paper.
Step 22: Fill a pastry bag with white icing and attach a large star tip to the end. Use the white icing to pipe a white band around the hat, and a white ball on the tip of the hat.
Step 23: Wipe the cake board one more time with a damp rag to make sure there is no extra icing or extra crumbs.
Step 24: Display your cake on your Christmas dessert table, or for a Grinch holiday party!