Several days in advance, using royal icing and 1 5/8 in. lily nail, make 70 tip 103 white petunias with tip 16 star centers; add stamens to centers and let dry. Using royal icing, make 275 tip 225 white drop flowers with tip 3 white dot centers. Make extras of all flowers to allow for breakage and let dry.
Ice 3 in. high square cake (stack two 1 1/2 in. high cakes) and 1-layer heart cake smooth in buttercream and prepare for
stacked construction. Divide top of square cake vertically and horizontally into 4ths, making sections approximately 3 1/2 in. square. Pipe tip 3 bead bottom border on heart cake and tip 5 bead bottom border on square cake. Attach drop flowers with icing at section marks on square cake.
Position petunias at base of square cake and on top of heart. Add tip 352 leaves on square cake in buttercream. Position leaves on heart cake. Enlarge lettering pattern to desired size; trace on cake with toothpick. Pipe monogram in buttercream using tips 1 and 3.