Coat six 4 1/2-inch individual tart pans with removable bottoms with cooking spray. Set aside.
Combine cracker crumbs and 3 tablespoons sugar in a medium bowl; stir well. Gradually add butter, stirring well. Stir in vanilla and egg white, stirring until well combined. Divide mixture evenly among tart pans; press mixture into bottom and up sides of pans. Place pans on a baking sheet. Bake at 350° for 13 minutes. Let cool completely on a wire rack.
Combine 2/3 cup sugar and cornstarch in a medium saucepan; stir well. Add lime juice and egg yolks, stirring with a whisk. Gradually add water, stirring well. Cook over medium heat, stirring constantly, 6 minutes or until mixture thickens. Remove from heat; stir in lime rind. Carefully pour into prepared crusts; let cool completely. Cover; chill at least 3 hours. Top each tart with 1 tablespoon whipped topping, and garnish with lime slices, if desired.
Lime Tart: Prepare crust as directed for Individual Lime Tarts, using a 9-inch tart pan with removable bottom. Bake at 350° for 15 minutes. Proceed with tart filling as directed.