Prepare and bake angel food cake mix according to package directions for a 10-inch tube pan. Cool as directed.
For icing, combine powdered sugar, hot water, and vanilla; if necessary, stir in additional water, 1 teaspoon at a time, to make the icing desired consistency. Spread icing over cake, allowing icing to run down sides of cake. Press cereal gently onto top. Makes 12 servings.