There’s nothing quite like an old-school Creamsicle from the ice cream truck — except maybe this jumbo version! To make the giant pop, we sandwiched orange sherbet between two layers of vanilla cake and covered it in a homemade marshmallow fondant. The oversize stick is just a wooden spatula!
Preheat the oven to 350˚ F. Prepare the cake mix as directed for a 9-by-13-inch cake; bake as directed. Let cool slightly in the pan, then remove to a rack to cool completely.
Transfer the cake to a baking sheet lined with parchment and carefully cut into 2 layers. Keeping the cakes stacked, trim a 3/4-inch strip from each long side. Reserve the trimmings (you’ll have 4 strips).
Cut off the carton from the sherbet and slice the block of sherbet lengthwise into thirds. Arrange on the bottom layer of the cake. Let soften slightly, then smooth with an offset spatula.
Use the 4 trimmed strips of cake to create a border all the way around the sherbet, breaking the pieces as needed. Cover with the top cake layer and freeze 1 hour.
Cut a large chunk out of one of the top corners of the cake to look like a bite. Trim the other top corner to make it rounded. Press a few of the cake trimmings against the exposed sherbet in the bite.
Using a paring knife, carve out 2 shallow channels in the cake as shown. Cover the top and sides of the cake with the frosting, making sure to cover the bite. Return the cake to the freezer.
Make the fondant: Put the marshmallows and water in a microwave-safe bowl; microwave, stirring occasionally, until melted and smooth. Tint orange with red and yellow food coloring. Transfer the mixture to a stand mixer.
Slowly beat all but 1/2 cup confectioners' sugar into the melted marshmallows (it will be stiff). Beat in the butter. Knead in some of the remaining sugar until rollable. Roll out on a confectioners' sugar–dusted surface until large enough to cover the entire cake.
Carefully drape the fondant over the cake and smooth with your hands. Trim the excess, cutting around the bite. Press a thin strip of fondant along the bottom of the bite. Insert a wooden spatula for the stick.