One day in advance, make sign. Using Brown icing color, tint 1½ oz. fondant dark brown; knead in 1 teaspoon Gum-Tex powder. Roll dark brown fondant to 1/8 in. thickness. Cut 2 in. x 4 in. rectangle, adding rough edges to short sides of sign. Using toothpick, imprint wood grain on sign. Using black FoodWriter marker, write “Carrots” on sign. Let sign dry on cooling grid, about 4 hours. Meanwhile, make fondant glue adhesive. To make adhesive, dissolve ¼ teaspoon white fondant in 1 tablespoon water. Let rest about 1 hour. Brush adhesive on back of sign. Place lollipop stick on back of sign. Roll small piece of white fondant into ½ in. x 1 in. log; press onto stick, making sure fondant comes in contact with adhesive to secure stick to fondant. Let dry, stick side up, overnight.
Make bunny feet and tail. Lightly dust bunny butt mold with cornstarch. Press 4 oz. white fondant into tail portion of bunny butt silicone mold. Unmold and set aside. Using Pink icing color, tint 1 oz. fondant pink. Roll six ½ in. balls and two ¾ in. balls of pink fondant; press ½ in. balls into small foot pads and ¾ in. balls into large foot pads. Reserve remaining pink fondant for later step. Using Brown icing color, tint 10 oz. fondant light brown. Roll 2 oz. light brown fondant into ball; slightly flatten and press into foot portion of bunny mold. Repeat with other foot. Reserve remaining light brown fondant for later step. Unmold feet and set aside.
Make carrots. Using Kelly Green icing color, tint ½ oz. fondant green; knead in ¼ teaspoon Gum-Tex powder. Set aside.Using Orange icing color, tint 1 oz. fondant orange. Divide into three portions; roll into balls. Roll green fondant into three ½ in. x 1 in. logs. Using scissors, cut slits into each log, defining leaves. Using fondant adhesive, attach leaves to carrots. Set aside.
Make mini bunnies. Prepare rice cereal treats following recipe instructions. Press rice cereal treats into seven bunny cavities on bunny treat mold, filling each ½ full. Freeze pan until set, about 20 minutes. Reserve remaining treat cereal for another project. Remove pan from freezer; immediately unmold bunnies. Let come to room temperature. Using Black icing color, tint 4 oz. fondant gray. Roll out to 1/8 in. thickness. Cover bunny faces with fondant. Repeat with remaining light brown fondant and 3 oz. white fondant. There should be two gray, three light brown and two white bunnies. Using black FoodWriter marker, draw on faces. For ears, roll reserved pink fondant into seven ¼ in. balls. Cut each ball in half; roll each half into ½ in. log, flattening slightly. Using damp brush, attach to outside of bunny ears. With remaining grey, light brown and white fondant, make bunny bodies. Divide gray fondant into two 1 oz. balls; knead in ¼ teaspoon Gum-Tex powder into each ball. Shape into ball, then taper top into cone shape, about ½ in. to ¾ in. tall. Repeat with remaining fondant, using 1 oz. fondant for each bunny body. Using remaining fondant glue adhesive (make more if necessary), attach heads to bodies. For tails, roll seven ½ in. balls of white fondant; press lightly to flatten. Using toothpick, indent fondant to make tail shape. Using damp brush, attach to bunny bodies.
Make cake. Prepare cake batter following recipe instructions. Bake and cool three layer cakes, trimming one to 1 in. high for a 5 in. high cake. Prepare cake for fondant covering. Using Lemon Yellow icing color, tint 36 oz. fondant yellow; cover cake. Reserve remaining yellow fondant for later step. Using Royal Blue icing color, tint 4 oz. fondant blue. Using 9 in. roller with purple guide rings, roll blue fondant 1/8 in. thick. Cut into 10 in. x 1½ in. strip. Brush back of strip with damp brush; attach to top of cake, leaving ¼ in. border above cake.
Decorate cake. Using Lemon Yellow icing color, tint ½ cup icing yellow. Lightly ice top of cake; top with crushed chocolate cookie crumbs. Using reserved yellow fondant, make fondant glue adhesive. While adhesive sits, position bunny feet on top of cake, cutting away blue fondant as necessary so feet sit flush with edge of cake. Use 1 in. ball yellow fondant to prop up feet. Brush yellow adhesive on back of bunny feet and ball of yellow fondant; attach to cake. Place 2 in. ball of yellow fondant in center of cake. Brush with adhesive and position bunny tale. Position carrots and sign in cake. Arrange bunnies around base of cake.