In advance: Make candy plaque castle. Fill castle pan with melted white candy, leaving background areas between turrets open. Refrigerate until firm; unmold. Reserve 3/4 cup of candy. Also: Make flowers and bushes using royal icing. Make 95 tip 225 drop flowers each in light and dark rose; add tip 2 dot centers in white. Make 25 tip 2D drop flowers in dark rose and 40 tip 129 drop flowers in light rose, each with tip 3 white dot centers. Make extra to allow for breakage and let dry. Make 2 tip 10 zigzag bushes on waxed paper-covered board. Attach tip 225 drop flowers; let dry. And: Using royal icing, ice tops of turrets smooth; sprinkle with Cake Sparkles. Outline and pipe in windows with tip 3 (pat smooth with finger dipped in cornstarch). Attach tip 225 drop flowers to turrets, window sills and around door with dots of royal icing. Add tip 349 leaves. Let dry. Trim 2 dowel rods to 9 in. Attach one full-length and two 9 in. dowel rods to back of candy plaque castle with melted candy, leaving 3 in.
extended at bottom to insert into cake. Let set.
Trace flag pattern on construction paper; cut 5 flags and attach to lollipop sticks with tape. Attach sticks to back of turrets with melted candy; let set.
Ice 2-layer cake smooth in buttercream (bake two 1 1/2 in. high layers to make a 3 in. high cake). Position on foil-wrapped base board. Pipe tip 6 bead top border and tip 32 shell bottom border. Attach tip 2D and tip 129 drop flowers at bottom border; add tip 349 leaves in buttercream. Print tip 3 message.
Insert castle in cake. Attach bushes with dots of icing. Position tip 225 drop flowers around cake top, arranging in semi-circles of 5 flowers.