Yields six (four-inch) sundaes.
Preheat oven to 350 degrees Fahrenheit. Grease six (four-inch) mini springform pans and set aside.
Beat the margarine in the bowl of an electric mixer at medium speed. Add the sugars and vanilla extract and beat until creamy. Add egg and milk and continue beating until light and fluffy.
Reduce mixer speed to low and add flour, cornstarch, baking soda, and salt. Stir in chocolate chips.
Divide dough evenly between the prepared pans and press down gently.
Bake for 25 minutes. It’s okay if the cookies are not done completely – they will have a fudgy consistency, not dry. Allow to cool completely.
This frosting can be made up to a week in advance and stored in the refrigerator. You could also prepare the frosting just before making the cookies, and chill it while the cookies are baking.
Beat the margarine in the bowl of an electric mixer.
Add half the sugar and the salt. Add whipped topping and mix until smooth. Add remaining sugar. Beat on high for two to three minutes, until frosting is light and fluffy.
Refrigerate frosting for one to two hours.
Using a large ice cream scoop, scoop cold frosting onto the cooled deep-dish cookies. Return to the refrigerator to chill while preparing the chocolate shell.
Combine chocolate chips and shortening in a microwave-safe bowl. Heat on high in the microwave for two minutes, stirring after every 30 seconds.
Transfer to a resealable plastic bag and snip off a small corner of the bag. Drizzle over the top of chilled “ice cream sundaes.”
Garnish with sprinkles and a cherry.
The sundaes can be frozen completely prepared. When defrosting, keep uncovered to allow the condensation to dry.