How to Make It
Preheat oven to 350°F. Lightly grease 3 (6-inch) round cake pans with cooking spray. Prepare cake mixes according to package directions. Pour batter evenly into prepared cake pans. Bake in preheated oven until a wooden pick inserted in center of each cake comes out clean, 20 to 22 minutes. Remove cakes from oven, and let cool for 10 minutes in pans on wire racks. Invert cakes onto cooling racks and cool completely, about 45 minutes.
Meanwhile, lightly dust work surface with cornstarch. Roll fuschia fondant on cornstarch (to prevent sticking) to a 1/8-inch-thick, 7-inch square. Using a sharp knife, cut 2 thin strips from 1 side of fondant square; set aside.
Using a sharp knife or a cookie cutter, cut rice treat into the shape of the number 1. Spread a very thin layer of frosting all over the 1 shape. Fold fuschia fondant square over frosted rice treat, cutting off excess and smoothing seam at the back. Use thin fondant strips to line the edge of fondant 1 shape, smoothing seams; discard excess. Stick an 8-inch lollipop stick in through the bottom of the fondant 1 shape; set aside.
Using a serrated knife, trim domed tops off of cooled cake layers. Trim 1 inch off the edge of 1 of the cake layers (making the 6-inch round a 4-inch round).
Assemble the cake: place 1 (6-inch) round on a cake plate. Spread top of cake layer with 1/2-inch-thick layer of blue frosting. Top with 4-inch cake round, and spread top with another 1/2-inch thick layer of frosting. Top the cake with remaining 6-inch cake round, and frost top of cake. Insert 2 to 3 dowel rods into cake to secure layers. Spread a very thin layer of frosting all over the cake, being sure to get edges and top as smooth as possible.
Lightly dust work surface with cornstarch. Massage blue fondant with hands, loosening and warming fondant as you go. Place fondant on dusted surface, and roll to 1/8-inch-thick, 18-inch round. Lay fondant over top of frosted cake, pressing and smoothing fondant down and around the cake as you go. Trim off any excess with a sharp knife.
Spread a very small amount of blue frosting on backs of dot icing decorations; adhere dots to cake. Place marshmallow fluff in a piping bag; pipe fluff around top and bottom of cake, allowing top fluff to slightly drip down the edges. Insert number 1 fondant into top of cake, and decorate with candles.