Coat a 2 1/2-quart ovenproof bowl with cooking spray. Prepare the cake mix as directed; pour into the bowl. Bake at 325 degrees F until a toothpick comes out clean, about 1 hour. Let cool completely.
Unmold the cake from the bowl and position rounded-side down. Using a long serrated knife, trim off the domed top to make the cake level.
Use a small serrated knife to cut a circle into the top of the cake, about 3/4 inch in from the edge and 1 1/2 inches deep. Use your fingers or a fork to pull out the cake in the middle.
Flip the cake over and place on a cardboard circle or plate lined with wax paper. Cover the rounded side with frosting, leaving the flat base unfrosted.
Cut out a small cardboard circle and place on the unfrosted base. Flip the cake over onto another piece of wax paper.
Frost the lip and the inside of the cake (the inside doesn't have to be perfect-it will be covered with ice cream). Transfer to the freezer until the frosting sets, 30 minutes.
Dip an offset spatula in hot water and wipe dry; smooth out the frosting.
Microwave the ice cream until softened but not melted. Scoop into the cavity of the cake and smooth with the spatula.
Sprinkle the cereal on top and gently press into the ice cream. Freeze until firm, at least 2 hours. Add a spoon before serving.
Photograph by Andrew Purcell
Courtesy of Food Network Magazine