Combine flour and salt in a 2-qt. heavy nonaluminum saucepan. Whisk in reduced-fat milk and next 3 ingredients, whisking until smooth. Cook over medium heat, whisking constantly, 10 to 12 minutes or until thickened. Remove from heat; stir in vanilla.
Fill a large bowl with ice; place pan in ice, and whisk custard occasionally until completely cool (about 30 minutes).
Spoon 1/2 cup custard into each of 8 (5-oz.) cups or glasses. Top each with 1 to 2 Tbsp. whipped topping, filling completely. Scrape top with a knife to level whipped topping. Garnish, if desired.
Note: To make ahead, pour cooled custard into a gallon-size zip-top plastic bag, gently pressing out excess air (to prevent a film from forming). Seal bag, and chill up to 24 hours. To serve, snip off 1 corner of bag, and pipe custard into serving cups.
Note: For testing purposes only, we used Nabisco 100 Calorie Packs Lorna Doone Shortbread Cookie Crisps.