Make roses one day in advance. Prepare royal icing following recipe directions. Divide icing and tint rose and green; reserve a small amount white. Set aside green and white icings covered in airtight containers. Use flower nail, icing flower squares, tips 7 and102, and rose icing to make 13 roses. Let dry overnight.
Make cake. Prepare batter following recipe directions. Bake and cool cake. Use knife or cake leveler to trim cake to 1 1/2 in. high. Use largest round Cut-Outs to cut 13 cake shapes.
Heat decorator icing in microwave at defrost setting (30% power) for 20-30 seconds; stir. Repeat until consistency of icing will pour. Place cakes on cooling grid positioned over parchment paper. Cover cakes with poured icing. Let dry 1 hour.
Decorate petits fours. Use white royal icing to attach white Sugar Pearls and roses to mini cakes. Use tip 352 and green royal icing to pipe leaves.
Use a cookie spatula and place petits fours on stand.