Make flowers two days in advance. Prepare buttercream icing following recipe directions. Tint a portion blue and reserve. Use tip 2D and white icing to make 95 swirl drop flowers on parchment paper-covered board. Make extras to allow for breakage. Use tip 3 and white icing to pipe a dot center on each flower. Attach a blue Sugar Pearl to center. Let air dry overnight.
Make cake one day in advance. Prepare batter following recipe directions. Bake and cool cake. Cake is 5 in. high (three layers: two 2 in. high, one 1 in. high). Place cake on foil-wrapped cake circle.
Ice and decorate cake. Use spatula and reserved blue icing to ice cake smooth. Use tip 18 and blue icing to pipe shell bottom border. Position flowers around top cake edge and in two rows around side, staggering bottom row. Position a single flower between each pair of flowers in bottom row. Position five flowers in a ring at center of cake top.