In a small saucepan combine brown sugar, corn syrup, and margarine. Cook and stir over medium heat until mixture boils. Remove from heat. Stir in flour and walnuts; beat until smooth.
Spoon 1 level tablespoon batter for each cookie, about 6 inches apart onto prepared cookie sheet. (Place 2 cookies on each sheet.)
Bake in a 375 degree F oven for 6 to 8 minutes or until cookies are set. Let cookies cool 1 to 2 minutes on baking sheet. (Cookies should be set but still flexible.) Remove carefully and drape cookies over inverted 6-ounce custard cups to cool. (If cookies are too firm to remove from baking sheets, place baking sheet back into oven for 15 to 20 seconds to soften.) Cool cookies completely. Let cookie sheet cool and spray with nonstick spray before baking 2 more cookies.
To serve, place scoops of ice milk or frozen yogurt in each cookie cup and top with Chocolate Dessert Sauce. Garnish with a cherry, if desired. Makes 8 servings.