1. Place oven racks in center and lower third of the oven; preheat oven to 350°F. Lightly spray 3 (8-inch-round) baking pans and 2 (6×3-inch-round) baking pans with nonstick cooking spray. Line pans with parchment paper and lightly spray with cooking spray. Set pans aside.  
2. Prepare cake batter according to package directions using water, oil and eggs. Pour 3 cups cake batter into each of 2 bowls; set aside. Pour 3 cups batter into one prepared 8-inch baking pan and 1½ cups batter into each prepared 6-inch baking pan; set aside.  
3. Stir 8 drops of yellow food coloring into one bowl of batter and 4 drops of yellow food coloring into the second bowl of batter. Pour each tinted batter into a separate prepared 8-inch baking pan.  
4. Place cake pans on both racks in oven. Bake the 6-inch cake layers for 26 to 30 minutes and 8-inch cake layers for 32 to 36 minutes, or until a toothpick inserted near centers comes out clean. Cool cakes in pans on wire racks for 10 minutes. Remove cakes from pans; remove parchment paper. Cool completely on wire racks.
5. Meanwhile, prepare Vanilla Buttercream; cover and set aside.
6. To assemble cake, trim and level tops of cake layers. Place the darkest yellow 8-inch cake layer on a pedestal cake plate; frost top with ¾ cup buttercream. Place the lighter yellow 8-inch cake layer on top; frost top with ¾ cup buttercream. Repeat with remaining 8-inch cake layer and ¾ cup frosting. Thinly frost side of 8-inch assembled cake with ¾ cup frosting. Set 8-inch assembled cake aside.
7. Place one 6-inch cake layer on a tray; frost top with ½ cup buttercream. Place remaining 6-inch cake layer on top; frost top with ½ cup buttercream. Thinly frost side of 6-inch assembled cake with remaining ¼ cup buttercream. Set 6-inch assembled cake aside.
8. Knead fondant until pliable.* Divide fondant in thirds; cover and set aside 1 portion. Roll out remaining 2 portions of fondant on a surface dusted with cornstarch or powdered sugar to ⅛-inch thickness using a fondant roller or rolling pin.
9. Drape fondant sheet over the 8-inch assembled cake, working from the back bottom edge of the cake, then up and over to the front bottom edge of the cake. Gently pull and stretch the fondant away from the cake to smooth side and remove creases. Trim and remove bottom excess fondant with a small sharp knife or kitchen scissors. Smooth or tuck bottom-cut edge underneath the cake. Set 8-inch assembled cake aside.
10. Roll out reserved portion of fondant on a surface dusted with cornstarch or powdered sugar to ⅛-inch thickness. Drape fondant over 6-inch assembled cake to cover. Smooth side and trim bottom edge; smooth or tuck bottom edge underneath the cake.
11. To give the cake more stability, if desired, insert cookie or lollipop sticks in a triangle shape, down through the center of the 8-inch assembled cake. Place 6-inch assembled cake on top of 8-inch cake. Decorate cake with ribbon and fondant flowers.

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*If light yellow fondant is not available, knead  6 drops of yellow food coloring into 32 ounces of white vanilla-flavor fondant.