Combine first 5 ingredients in a large bowl, stirring with a whisk until smooth; pour into the top of a double boiler. Cook over simmering water until mixture thickens (about 6 minutes) or until a thermometer registers 160°, stirring constantly. Remove from heat. Place pan in a large ice-filled bowl for 20 minutes or until mixture comes to room temperature, stirring occasionally.
Spoon 1 tablespoon whipped cream into each of 8 (8-ounce) glasses; top each serving with 1 tablespoon crumbs and 3 tablespoons lime mixture. Repeat layers once, ending with lime mixture. Top each serving with 1 tablespoon whipped cream; sprinkle with lime rind, if desired. Serve immediately.