Whisk together first 4 ingredients in a small nonaluminum saucepan over medium-low heat, and cook, stirring constantly, 15 minutes or until slightly thickened. (Mixture should lightly coat the back of a spoon.) Remove from heat; stir in vanilla.
Pour mixture into a small mixing bowl, and place plastic wrap directly over surface of custard to prevent film from forming; chill 2 hours or until ready to serve.
Layer fruit and cake in 8 mason jars or tall glasses. Drizzle each with 1/4 cup vanilla sauce. Garnish, if desired.