Make cupcakes. Prepare batter following recipe directions. Bake and cool cupcakes.
Ice cupcakes. Prepare buttercream icing following recipe directions. Use spatula and icing to ice cupcakes smooth.
Make marshmallow flowers. For each flower, cut four horizontal slits in marshmallow, 3/4 of the way across. Fan out each marshmallow section and shape with fingers to form a circle of five petals.
For center, cut one horizontal slice, 1/4 in. high, from top of another marshmallow. Dip slice in cornstarch to prevent sticking. Flatten slightly with fingers. Roll into a cone shape. Use brush and piping gel to secure ends. Trim tip of cone and use fingers to open top slightly. Use brush and piping gel to attach center to flower.
Decorate marshmallow flowers. Place flower on parchment-covered board. Use orange, pink or yellow food color spray to cover flower. Let dry, about 10 to 15 minutes.